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

vendor/assets/javascripts/mousetrap-global-bind.js

@@ -0,0 +1,43 @@
+/**
+ * adds a bindGlobal method to Mousetrap that allows you to
+ * bind specific keyboard shortcuts that will still work
+ * inside a text input field
+ *
+ * usage:
+ * Mousetrap.bindGlobal('ctrl+s', _saveChanges);
+ */
+/* global Mousetrap:true */
+(function(Mousetrap) {
+    var _globalCallbacks = {};
+    var _originalStopCallback = Mousetrap.prototype.stopCallback;
+
+    Mousetrap.prototype.stopCallback = function(e, element, combo, sequence) {
+        var self = this;
+
+        if (self.paused) {
+            return true;
+        }
+
+        if (_globalCallbacks[combo] || _globalCallbacks[sequence]) {
+            return false;
+        }
+
+        return _originalStopCallback.call(self, e, element, combo);
+    };
+
+    Mousetrap.prototype.bindGlobal = function(keys, callback, action) {
+        var self = this;
+        self.bind(keys, callback, action);
+
+        if (keys instanceof Array) {
+            for (var i = 0; i < keys.length; i++) {
+                _globalCallbacks[keys[i]] = true;
+            }
+            return;
+        }
+
+        _globalCallbacks[keys] = true;
+    };
+
+    Mousetrap.init();
+}) (Mousetrap);