Move platform to common and remove dom dependence in common

Because common/ imports 'xterm', it also imported dom accidentally.

Fixes #1990

src/core/Platform.ts

@@ -1,30 +0,0 @@
-/**
- * Copyright (c) 2016 The xterm.js authors. All rights reserved.
- * @license MIT
- */
-
-const isNode = (typeof navigator === 'undefined') ? true : false;
-const userAgent = (isNode) ? 'node' : navigator.userAgent;
-const platform = (isNode) ? 'node' : navigator.platform;
-
-export const isFirefox = !!~userAgent.indexOf('Firefox');
-export const isSafari = /^((?!chrome|android).)*safari/i.test(userAgent);
-export const isMSIE = !!~userAgent.indexOf('MSIE') || !!~userAgent.indexOf('Trident');
-
-// Find the users platform. We use this to interpret the meta key
-// and ISO third level shifts.
-// http://stackoverflow.com/q/19877924/577598
-export const isMac = contains(['Macintosh', 'MacIntel', 'MacPPC', 'Mac68K'], platform);
-export const isIpad = platform === 'iPad';
-export const isIphone = platform === 'iPhone';
-export const isMSWindows = contains(['Windows', 'Win16', 'Win32', 'WinCE'], platform);
-export const isLinux = platform.indexOf('Linux') >= 0;
-
-/**
- * Return if the given array contains the given element
- * @param arr The array to search for the given element.
- * @param el The element to look for into the array
- */
-function contains(arr: any[], el: any): boolean {
-  return arr.indexOf(el) >= 0;
-}

src/core/tsconfig.json

@@ -4,7 +4,7 @@
     "outDir": "../../lib"
   },
   "include": [
-    "./**/*"
+    "./**/*", "../common/Platform.ts"
   ],
   "references": [
     { "path": "../common" }