Move Shared interfaces into a new typings file

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

src/utils/CharMeasure.test.ts

@@ -4,8 +4,8 @@
  */
 
 import jsdom = require('jsdom');
+import { ICharMeasure, ITerminal } from '../../typings/xterm-internal';
 import { assert } from 'chai';
-import { ICharMeasure, ITerminal } from '../Interfaces';
 import { CharMeasure } from './CharMeasure';
 
 describe('CharMeasure', () => {

src/utils/CharMeasure.ts

@@ -3,8 +3,8 @@
  * @license MIT
  */
 
+import { ICharMeasure, ITerminal, ITerminalOptions } from '../../typings/xterm-internal';
 import { EventEmitter } from '../EventEmitter';
-import { ICharMeasure, ITerminal, ITerminalOptions } from '../Interfaces';
 
 /**
  * Utility class that measures the size of a character. Measurements are done in

src/utils/CircularList.ts

@@ -4,7 +4,7 @@
  */
 
 import { EventEmitter } from '../EventEmitter';
-import { ICircularList } from '../Interfaces';
+import { ICircularList } from '../../typings/xterm-internal';
 
 /**
  * Represents a circular list; a list with a maximum size that wraps around when push is called,

src/utils/MouseHelper.ts

@@ -3,8 +3,7 @@
  * @license MIT
  */
 
-import { ICharMeasure } from '../Interfaces';
-import { IRenderer } from '../renderer/Interfaces';
+import { ICharMeasure, IRenderer } from '../../typings/xterm-internal';
 
 export class MouseHelper {
   constructor(private _renderer: IRenderer) {}
@@ -24,7 +23,7 @@ export class MouseHelper {
     while (element) {
       x -= element.offsetLeft;
       y -= element.offsetTop;
-      element = 'offsetParent' in element ? <HTMLElement>element.offsetParent : <HTMLElement>element.parentElement;
+      element = <HTMLElement>element.offsetParent;
     }
     element = originalElement;
     while (element && element !== element.ownerDocument.body) {

src/utils/TestUtils.test.ts

@@ -3,11 +3,11 @@
  * @license MIT
  */
 
-import { ITerminal, IBuffer, IBufferSet, IBrowser, ICharMeasure, ISelectionManager, ITerminalOptions, IInputHandlingTerminal, IViewport, ICircularList, ICompositionHelper, ITheme, ILinkifier, IMouseHelper, ILinkMatcherOptions } from '../Interfaces';
-import { LineData } from '../Types';
+import { ITerminal, IBuffer, IBufferSet, IBrowser, ICharMeasure, ISelectionManager, ITerminalOptions, ICircularList, ITheme, ILinkifier, IMouseHelper, ILinkMatcherOptions, LineData, IColorSet, IRenderer, IRenderDimensions, IColorManager } from '../../typings/xterm-internal';
+import { IInputHandlingTerminal, IViewport, ICompositionHelper } from '../Interfaces';
+import {  } from '../Types';
 import { Buffer } from '../Buffer';
 import * as Browser from './Browser';
-import { IColorSet, IRenderer, IRenderDimensions, IColorManager } from '../renderer/Interfaces';
 
 export class MockTerminal implements ITerminal {
   getOption(key: any): any {