Replace add userby email textinput in admin/roles#show with searchable combobox

app/assets/javascripts/application.js

@@ -40,6 +40,8 @@
 //= require osem-commercials
 //= require unobtrusive_flash
 //= require unobtrusive_flash_bootstrap
+//= require bootstrap-select
+//= require osem-selectpicker
 
 $(document).ready(function() {
     $('a[disabled=disabled]').click(function(event){

app/assets/javascripts/osem-selectpicker.js

@@ -0,0 +1,3 @@
+$(function () {
+  $('.selectpicker').selectpicker();
+});