Edit Data Service (#241)

This is a very large change. I'll try to outline what's going on.

1. This adds the **EditDataService** which manages editing **Sessions**.
    1. Each session has a **ResultSet** (from the QueryExecutionService) which has the rows of the table and basic metadata about the columns 
    2. Each session also has an **IEditTableMetadata** implementation which is derived from SMO metadata which provides more in-depth and trustworthy data about the table than SqlClient alone can.
    3. Each session holds a list of **RowEditBase** abstract class implementations
        1. **RowUpdate** - Update cells in a row (generates `UPDATE` statement)
        2. **RowDelete** - Delete an entire row (generates `DELETE` statement)
        3. **RowCreate** - Add a new row (generates `INSERT INTO` statement)
    4. Row edits have a collection of **CellUpdates** that hold updates for individual cells (except for RowDelete)
        1. Cell updates are generated from text
     5. RowEditBase offers some baseline functionality
        1. Generation of `WHERE` clauses (which can be parameterized)
        2. Validation of whether a column can be updated
2. New API Actions
    1. edit/initialize - Queries for the contents of a table/view, builds SMO metadata, sets up a session
    2. edit/createRow - Adds a new RowCreate to the Session
    3. edit/deleteRow - Adds a new RowDelete to the Session
    4. edit/updateCell - Adds a CellUpdate to a RowCreate or RowUpdate in the Session
    5. edit/revertRow - Removes a RowCreate, RowDelete, or RowUpdate from the Session
    6. edit/script - Generates a script for the changes in the Session and stores to disk
    7. edit/dispose - Removes a Session and releases the query
3. Smaller updates (unit test mock improvements, tweaks to query execution service)

**There are more updates planned -- this is just to get eyeballs on the main body of code**

* Initial stubs for edit data service

* Stubbing out update management code

* Adding rudimentary dispose request

* More stubbing out of update row code

* Adding complete edit command contracts, stubbing out request handlers

* Adding basic implementation of get script

* More in progress work to implement base of row edits

* More in progress work to implement base of row edits

* Adding string => object conversion logic and various cleanup

* Adding a formatter for using values in scripts

* Splitting IMessageSender into IEventSender and IRequestSender

* Adding inter-service method for executing queries

* Adding inter-service method for disposing of a query

* Changing edit contract to include the object to edit

* Fully fleshing out edit session initialization

* Generation of delete scripts is working

* Adding scripter for update statements

* Adding scripting functionality for INSERT statements

* Insert, Update, and Delete all working with SMO metadata

* Polishing for SqlScriptFormatter

* Unit tests and reworked byte[] conversion

* Replacing the awful and inflexible Dictionary<string, string>[][] with a much better test data set class

* Fixing syntax error in generated UPDATE statements

* Adding unit tests for RowCreate

* Adding tests for the row edit base class

* Adding row delete tests

* Adding RowUpdate tests, validation for number of key columns

* Adding tests for the unit class

* Adding get script tests for the session

* Service integration tests, except initialization tests

* Service integration tests, except initialization tests

* Adding messages to sr.strings

* Adding messages to sr.strings

* Fixing broken unit tests

* Adding factory pattern for SMO metadata provider

* Copyright and other comments

* Addressing first round of comments

* Refactoring EditDataService to have a single method for handling
session-dependent operations
* Refactoring Edit Data contracts to inherit from a Session and Row
operation params base class
* Copyright additions
* Small tweak to strings
* Updated unit tests to test the refactors

* More revisions as per pull request comments

src/Microsoft.SqlTools.ServiceLayer/EditData/Contracts/EditInitializeRequest.cs

@@ -0,0 +1,42 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using Microsoft.SqlTools.ServiceLayer.Hosting.Protocol.Contracts;
+
+namespace Microsoft.SqlTools.ServiceLayer.EditData.Contracts
+{
+    /// <summary>
+    /// Parameters of the edit session initialize request
+    /// </summary>
+    public class EditInitializeParams : SessionOperationParams
+    {
+        /// <summary>
+        /// The object to use for generating an edit script
+        /// </summary>
+        public string ObjectName { get; set; }
+
+        /// <summary>
+        /// The type of the object to use for generating an edit script
+        /// </summary>
+        public string ObjectType { get; set; }
+    }
+
+    /// <summary>
+    /// Object to return upon successful completion of an edit session initialize request
+    /// </summary>
+    /// <remarks>
+    /// Empty for now, since there isn't anything special to return on success
+    /// </remarks>
+    public class EditInitializeResult
+    {
+    }
+
+    public class EditInitializeRequest
+    {
+        public static readonly 
+            RequestType<EditInitializeParams, EditInitializeResult> Type =
+            RequestType<EditInitializeParams, EditInitializeResult>.Create("edit/initialize");
+    }
+}