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/.vscode/launch.json

@@ -0,0 +1,57 @@
+// A launch configuration that launches the extension inside a new window
+// Use IntelliSense to learn about possible attributes.
+// Hover to view descriptions of existing attributes.
+// For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
+
+// To debug the extension:
+// 1. please install the "SQL Operations Studio Debug" extension into VSCode
+// 2. Ensure sqlops is added to your path:
+//    - open SQL Operations Studio
+//    - run the command "Install 'sqlops' command in PATH"
+{
+	"version": "0.2.0",
+    "configurations": [
+
+        {
+            "name": "Debug in SqlOps install",
+            "type": "sqlopsExtensionHost",
+            "request": "launch",
+            "runtimeExecutable": "sqlops",
+            "args": [
+                "--extensionDevelopmentPath=${workspaceFolder}"
+            ]
+        },
+		{
+			"type": "node",
+			"request": "attach",
+			"name": "Attach to Ops Studio",
+			"protocol": "inspector",
+			"port": 5870,
+			"restart": true,
+            "sourceMaps": true,
+			"outFiles": [
+				"${workspaceRoot}/out/**/*.js"
+			],
+            "preLaunchTask": "",
+            "timeout": 25000
+		},
+        {
+            "name": "Debug in enlistment",
+            "type": "sqlopsExtensionHost",
+            "request": "launch",
+			"windows": {
+				"runtimeExecutable": "${workspaceFolder}/../../scripts/sql.bat"
+			},
+			"osx": {
+				"runtimeExecutable": "${workspaceFolder}/../../scripts/sql.sh"
+			},
+			"linux": {
+				"runtimeExecutable": "${workspaceFolder}/../../scripts/sql.sh"
+			},
+            "args": [
+                "--extensionDevelopmentPath=${workspaceFolder}"
+            ],
+            "timeout": 20000
+        }
+    ]
+}

samples/sqlservices/.vscode/tasks.json

@@ -0,0 +1,14 @@
+{
+    // See https://go.microsoft.com/fwlink/?LinkId=733558
+    // for the documentation about the tasks.json format
+    "version": "2.0.0",
+    "tasks": [
+        {
+            "type": "gulp",
+            "task": "build",
+            "problemMatcher": [
+                "$gulp-tsc"
+            ]
+        }
+    ]
+}