Extensibility: Context menu support in Object Explorer (#1883)

- Fixes #1867 context menu should be extensible
- Added context keys to support "when" conditions on the new extensions
- Fixes issue where actions like New Query, scripting show up even if these are not valid for the provider type or object type
- Fixed node expansion bug where rapid connect / expand / disconnect could break the app (fix in ObjectExplorerService.onNodeExpanded)
- Major change to how internal actions work. These cannot assume the context has non-serializable objects. Opened up some APIs to make this easier to handle.
- Fixed a number of existing bugs in internal actions.
  - Notably, DisconnectAction was adding a listener on each right-click on an active connection and never getting it disposed. This wasn't needed at all due to design changes.
  - Another bug fix is that the Manage action now correctly navigates to the DB dashboard for database-level connections. Before this it went to the server-level dashboard.

* Define API for context info

src/sql/services/common/commonServiceInterface.service.ts

@@ -17,7 +17,7 @@ import { IAdminService } from 'sql/parts/admin/common/adminService';
 import { IQueryManagementService } from 'sql/parts/query/common/queryManagement';
 import { IConnectionProfile } from 'sql/parts/connection/common/interfaces';
 import { AngularDisposable } from 'sql/base/common/lifecycle';
-import { ConnectionContextkey } from 'sql/parts/connection/common/connectionContextKey';
+import { ConnectionContextKey } from 'sql/parts/connection/common/connectionContextKey';
 
 import { ProviderMetadata, DatabaseInfo, SimpleExecuteResult } from 'sqlops';
 
@@ -47,7 +47,7 @@ export class SingleConnectionManagementService {
 	constructor(
 		private _connectionService: IConnectionManagementService,
 		private _uri: string,
-		private _contextKey: ConnectionContextkey
+		private _contextKey: ConnectionContextKey
 	) { }
 
 	public changeDatabase(name: string): Thenable<boolean> {
@@ -104,7 +104,7 @@ export class CommonServiceInterface extends AngularDisposable {
 	protected _singleQueryManagementService: SingleQueryManagementService;
 	public scopedContextKeyService: IContextKeyService;
 
-	protected _connectionContextKey: ConnectionContextkey;
+	protected _connectionContextKey: ConnectionContextKey;
 
 	constructor(
 		@Inject(IBootstrapParams) protected _params: IDefaultComponentParams,