Move Shared interfaces into a new typings file

This will enable sharing the internal interface with addons (and catching
breakages early)

src/input/Interfaces.ts

@@ -1,19 +0,0 @@
-/**
- * Copyright (c) 2017 The xterm.js authors. All rights reserved.
- * @license MIT
- */
-
-export interface IMouseZoneManager {
-  add(zone: IMouseZone): void;
-  clearAll(start?: number, end?: number): void;
-}
-
-export interface IMouseZone {
-  x1: number;
-  x2: number;
-  y: number;
-  clickCallback: (e: MouseEvent) => any;
-  hoverCallback?: (e: MouseEvent) => any;
-  tooltipCallback?: (e: MouseEvent) => any;
-  leaveCallback?: () => any;
-}

src/input/MouseZoneManager.ts

@@ -3,8 +3,7 @@
  * @license MIT
  */
 
-import { IMouseZoneManager, IMouseZone } from './Interfaces';
-import { ITerminal } from '../Interfaces';
+import { IMouseZoneManager, IMouseZone, ITerminal } from '../../typings/xterm-internal';
 
 const HOVER_DURATION = 500;