Cancel quick-search on Escape, clearing it and returning focus to composer.

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

src/components/structures/SearchBox.js

@@ -100,6 +100,10 @@ module.exports = React.createClass({
         }
 
         switch (ev.keyCode) {
+            case KeyCode.ESCAPE:
+                this._clearSearch();
+                dis.dispatch({action: 'focus_composer'});
+                break;
             case KeyCode.KEY_K:
                 if (ctrlCmdOnly) {
                     if (this.refs.search) {