Feat/model backed ui (#1145)

This is an initial PR for a new model-driven UI where extensions can provide definitions of the components & how they're laid out using Containers.
#1140, #1141, #1142, #1143 and #1144 are all tracking additional work needed to improve the initial implementation and fix some issues with the implementation.

Features:
- Supports defining a FlexContainer that maps to a flexbox-based layout.
- Supports creating a card component, which is a key-value pair based control that will lay out simple information to a user. Eventually this will have an optional set of actions associated with it.
- Has a sample project which shows how to use the API and was used for verification

samples/sqlservices/tasks/config.js

@@ -0,0 +1,24 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the Source EULA. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+var path = require('path');
+
+var projectRoot = path.resolve(path.dirname(__dirname));
+var srcRoot = path.resolve(projectRoot, 'src');
+var localization = path.resolve(projectRoot, 'localization');
+
+var config = {
+    paths: {
+        project: {
+            root: projectRoot,
+            localization: localization
+        },
+        extension: {
+            root: srcRoot
+        }
+    }
+};
+
+module.exports = config;