Refactor char atlas to enable generation with worker

This doesn't actually add workers but it separates the code nicely
such that the minimal amount of relevant code can be pulled in by
worker code.

Part of #955

src/shared/utils/Browser.ts

@@ -0,0 +1,29 @@
+/**
+ * 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 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 {Array} array The array to search for the given element.
+ * @param {Object} el The element to look for into the array
+ */
+export function contains(arr: any[], el: any): boolean {
+  return arr.indexOf(el) >= 0;
+};