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/src/utils.ts

@@ -0,0 +1,52 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the Source EULA. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+'use strict';
+
+import * as fs from 'fs-extra';
+import * as handlebars from 'handlebars';
+import * as path from 'path';
+import * as vscode from 'vscode';
+
+import * as Constants from './constants';
+import * as nls from 'vscode-nls';
+
+const localize = nls.loadMessageBundle();
+
+/**
+ * Helper to log messages to the developer console if enabled
+ * @param msg Message to log to the console
+ */
+export function logDebug(msg: any): void {
+	let config = vscode.workspace.getConfiguration(Constants.extensionConfigSectionName);
+	let logDebugInfo = config[Constants.configLogDebugInfo];
+	if (logDebugInfo === true) {
+		let currentTime = new Date().toLocaleTimeString();
+		let outputMsg = '[' + currentTime + ']: ' + msg ? msg.toString() : '';
+		console.log(outputMsg);
+	}
+}
+
+export function renderTemplateHtml(extensionPath: string, templateName: string, templateValues: object): Thenable<string> {
+	let templatePath = path.join(extensionPath, 'resources', templateName);
+
+	// 1) Read the template from the disk
+	// 2) Compile it as a handlebars template and render the HTML
+	// 3) On failure, return a simple string as an error
+	return fs.readFile(templatePath, 'utf-8')
+		.then(templateText => {
+			let template = handlebars.compile(templateText);
+			return template(templateValues);
+		})
+		.then(
+			undefined,
+			error => {
+				logDebug(error);
+				return localize('errorLoadingTab', 'An error occurred while loading the tab');
+			}
+		);
+}
+
+