Refactor composite bar

- Create a composite model
- Show the context menu in the same order
- Retain the position after unpin

src/vs/workbench/browser/parts/activitybar/activitybarPart.ts

@@ -182,6 +182,11 @@ export class ActivitybarPart extends Part {
 			const canShow = this.canShow(viewlet);
 			if (canShow) {
 				this.compositeBar.addComposite(viewlet, false);
+				const activeViewlet = this.viewletService.getActiveViewlet();
+				if (activeViewlet && activeViewlet.getId() === viewlet.id) {
+					this.compositeBar.pin(viewlet.id);
+					this.compositeBar.activateComposite(viewlet.id);
+				}
 			} else {
 				this.compositeBar.removeComposite(viewlet.id);
 			}

src/vs/workbench/browser/parts/panel/panelPart.ts

@@ -172,6 +172,10 @@ export class PanelPart extends CompositePart<Panel> implements IPanelService {
 			descriptor.enabled = enabled;
 			if (enabled) {
 				this.compositeBar.addComposite(descriptor, true);
+				this.openPanel(descriptor.id, true).done(() => {
+					this.compositeBar.pin(descriptor.id);
+					this.compositeBar.activateComposite(descriptor.id);
+				});
 			} else {
 				this.compositeBar.removeComposite(id);
 			}

src/vs/workbench/parts/output/browser/outputPanel.ts

@@ -49,6 +49,10 @@ export class OutputPanel extends AbstractTextResourceEditor {
 		return OUTPUT_PANEL_ID;
 	}
 
+	public getTitle(): string {
+		return nls.localize('output', "Output");
+	}
+
 	public getActions(): IAction[] {
 		if (!this.actions) {
 			this.actions = [