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

src/sql/parts/dashboard/containers/dashboardErrorContainer.component.ts

@@ -39,7 +39,7 @@ export class DashboardErrorContainer extends DashboardTab implements AfterViewIn
 
 	ngAfterViewInit() {
 		let errorMessage = this._errorMessageContainer.nativeElement as HTMLElement;
-		errorMessage.innerHTML = nls.localize('dashboardNavSection_loadTabError', 'The {0} has an invalid content. Please contact extension owner.', this.tab.title);
+		errorMessage.innerHTML = nls.localize('dashboardNavSection_loadTabError', 'The "{0}" section has invalid content. Please contact extension owner.', this.tab.title);
 	}
 
 	public get id(): string {