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/tsconfig.json

@@ -0,0 +1,16 @@
+{
+    "compileOnSave": true,
+    "compilerOptions": {
+        "module": "commonjs",
+        "target": "ES6",
+        "lib": [ "es6" ],
+        "sourceMap": true,
+        "emitDecoratorMetadata": true,
+        "experimentalDecorators": true,
+        "rootDir": "."
+    },
+    "exclude": [
+        "node_modules",
+        ".vscode-test"
+    ]
+}