Handle window resize events in React way

Use the React-way of handling resize events. Essentially store the window size in component state instead of doing some custom handling.

See http://facebook.github.io/react/tips/dom-event-listeners.html

web/react/utils/utils.jsx

@@ -968,3 +968,11 @@ export function getShortenedTeamURL() {
     }
     return teamURL + '/';
 }
+
+export function windowWidth() {
+    return $(window).width();
+}
+
+export function windowHeight() {
+    return $(window).height();
+}