Remove SELECT * from edit/initialize Query (#288)

* Major refactor of EditDataMetadata providers

* EditMetadataFactory generates "basic" EditTableMetadata objects based entirely on SMO metadata
* SmoEditTableMetadata no longer depends on SMO, making it unecessary to mock it
* Renamed SmoEditTableMetadata to EditTableMetadata
* EditTableMetadata can be extended with DbColumnWrappers

* Moving logic for extending a EditColumnMetadata into that class

* I *think* this will work for async execution of initialize tasks

* Fixing unit tests for new Edit(Table|Column)Metadata classes

* Async stuff that works! And passes unit tests

* Adding unit tests
Adding .idea to gitignore

* Adding message to the EditSessionReadyEvent

* Fixes from dev merge

* Fixing unit tests that Rider didn't catch as failing
May have been a bit heavy-handed with the async/await stuff

* Couple changes as per PR comments

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

@@ -14,6 +14,12 @@ namespace Microsoft.SqlTools.ServiceLayer.EditData.Contracts
         /// </summary>
         public string OwnerUri { get; set; }
 
+        /// <summary>
+        /// Message to explain why a session failed. Should only be set when <see cref="Success"/>
+        /// is <c>false</c>.
+        /// </summary>
+        public string Message { get; set; }
+
         /// <summary>
         /// Whether or not the session is ready
         /// </summary>