FIX: make composer full screen shortcut work when inputs have focus (#6907)

- Uses a Mousetrap plugin for global shortcuts
- Implemented for search `ctrl+alt+f` and composer fullscreen `shift+f11` shortcuts

app/assets/javascripts/vendor.js

@@ -22,6 +22,7 @@
 //= require jquery.sortable.js
 //= require lodash.js
 //= require mousetrap.js
+//= require mousetrap-global-bind.js
 //= require rsvp.js
 //= require show-html.js
 //= require break_string