Move duplicate js functionality into IssuableForm

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/assets/javascripts/dispatcher.js.coffee

@@ -31,19 +31,13 @@ class Dispatcher
       when 'projects:compare:show'
         new Diff()
       when 'projects:issues:new','projects:issues:edit'
-        GitLab.GfmAutoComplete.setup()
         shortcut_handler = new ShortcutsNavigation()
-        new ZenMode()
         new DropzoneInput($('.issue-form'))
-        if page == 'projects:issues:new'
         new IssuableForm($('.issue-form'))
       when 'projects:merge_requests:new', 'projects:merge_requests:edit'
-        GitLab.GfmAutoComplete.setup()
         new Diff()
         shortcut_handler = new ShortcutsNavigation()
-        new ZenMode()
         new DropzoneInput($('.merge-request-form'))
-        if page == 'projects:merge_requests:new'
         new IssuableForm($('.merge-request-form'))
       when 'projects:merge_requests:show'
         new Diff()

app/assets/javascripts/issuable_form.js.coffee

 class @IssuableForm
   constructor: (@form) ->
+    GitLab.GfmAutoComplete.setup()
+    new UsersSelect()
+    new ZenMode()
+
     @titleField       = @form.find("input[name*='[title]']")
     @descriptionField = @form.find("textarea[name*='[description]']")