Add noUnusedLocals tsconfig flag, fix issues

Two parts were commented out:
- _writeStopped: This is because _xoffSentToCatchUp references this variable
  and the feature is sort of half implemented/disabled.
- _clearChar: This is because some comments still reference this, it's part
  of the work needed to do better line redrawing.

src/Types.ts

@@ -3,7 +3,7 @@
  * @license MIT
  */
 
-import { Terminal as PublicTerminal, ITerminalOptions as IPublicTerminalOptions, IEventEmitter as IPublicEventEmitter, IEventEmitter } from 'xterm';
+import { Terminal as PublicTerminal, ITerminalOptions as IPublicTerminalOptions, IEventEmitter } from 'xterm';
 import { IColorSet, IRenderer } from './renderer/Types';
 import { IMouseZoneManager } from './input/Types';
 
@@ -84,6 +84,7 @@ export interface IInputHandlingTerminal extends IEventEmitter {
   matchColor(r1: number, g1: number, b1: number): number;
   error(text: string, data?: any): void;
   setOption(key: string, value: any): void;
+  tabSet(): void;
 }
 
 export interface IViewport {