Dashboard custom buttons

Implement #17 (closed): Custom buttons for dashboard

Update fontawesome dependency to version 5

• less dependencies (no more select-2 and special jQuery version)
• current icons
• admin widget working

The update required changes in the templates (new template tag and version 5 introduced namespacing for styles)

Fix design issue in dashboard

AKDashboard/locale/de_DE/LC_MESSAGES/django.po

@@ -19,7 +19,7 @@ msgstr ""
 
 #: models.py:10
 msgid "Dashboard Button"
-msgstr "Dasbhoard-Button"
+msgstr "Dashboard-Button"
 
 #: models.py:11
 msgid "Dashboard Buttons"