WebSocket-Resources / websocket refactor

This commit provides the javascript complement to
[WebSocket-Resources](https://github.com/WhisperSystems/WebSocket-Resources),
allowing us to use a bi-directional request-response framework over
websockets.

See websocket-resources.js and websocket-resources_test.js
for usage details.

Along the way I also factored the websocket keepalive and reconnect
logic into its own file/wrapper object.

js/websocket.js

@@ -0,0 +1,72 @@
+/* vim: ts=4:sw=4:expandtab
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+;(function(){
+    'use strict';
+
+    /*
+     * var socket = textsecure.websocket(url);
+     *
+     * Returns an adamantium-reinforced super socket, capable of sending
+     * app-level keep alives and automatically reconnecting.
+     *
+     */
+
+    window.textsecure.websocket = function (url) {
+        var socketWrapper = { onmessage: function() {}, ondisconnect: function() {} };
+        var socket;
+        var keepAliveTimer;
+        var reconnectSemaphore = 0;
+        var reconnectTimeout = 1000;
+
+        function resetKeepAliveTimer() {
+            clearTimeout(keepAliveTimer);
+            keepAliveTimer = setTimeout(function() {
+                socket.send(JSON.stringify({type: 1, id: 0}));
+                resetKeepAliveTimer();
+            }, 50000);
+        };
+
+        function reconnect(e) {
+            reconnectSemaphore--;
+            setTimeout(connect, reconnectTimeout);
+            socketWrapper.ondisconnect(e);
+        };
+
+        var connect = function() {
+            clearTimeout(keepAliveTimer);
+            if (++reconnectSemaphore <= 0) { return; }
+
+            if (socket) { socket.close(); }
+            socket = new WebSocket(url);
+
+            socket.onerror = reconnect;
+            socket.onclose = reconnect;
+            socket.onopen  = resetKeepAliveTimer;
+
+            socket.onmessage = function(response) {
+                socketWrapper.onmessage(response);
+                resetKeepAliveTimer();
+            };
+
+            socketWrapper.send = function(msg) {
+                socket.send(msg);
+            }
+        };
+
+        connect();
+        return socketWrapper;
+    };
+})();