enhanced plugin support (#634)

- refactored admin controller and templates
- plugin support for entity actions
- changed column mail to email in customer table
- refactored theme events

templates/export/renderer/default.html.twig

@@ -91,8 +91,8 @@
         'label.activity',
         'label.description',
         'label.exported',
-        'label.hourly_rate',
-        'label.fixed_rate',
+        'label.hourlyRate',
+        'label.fixedRate',
         'label.duration',
         'label.rate',
     ] %}