FIX: select-kit refactoring

- improve mini-tag-chooser keyboard behavior
- all multil select now respond to select all and left/right arrows
- improve events handling
- many minor tweaks

app/assets/javascripts/select-kit/components/composer-actions.js.es6

@@ -45,7 +45,7 @@ export default DropdownSelectBoxComponent.extend({
   },
 
   computeHeaderContent() {
-    let content = this.baseHeaderComputedContent();
+    let content = this._super();
 
     switch (this.get("action")) {
       case PRIVATE_MESSAGE: