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/activity/edit.html.twig

@@ -0,0 +1,15 @@
+{% extends app.request.xmlHttpRequest ? 'form.html.twig' : 'base.html.twig' %}
+{% import "macros/widgets.html.twig" as widgets %}
+{% import "macros/actions.html.twig" as actions %}
+
+{% block page_title %}{{ 'admin_activity.title'|trans }}{% endblock %}
+{% block page_subtitle %}{{ 'admin_activity.subtitle'|trans }}{% endblock %}
+{% block page_actions %}{{ actions.activity(activity, 'edit') }}{% endblock %}
+
+{% block main %}
+    {{ include(app.request.xmlHttpRequest ? 'default/_form_modal.html.twig' : 'default/_form.html.twig', {
+        'title': activity.name|default('create'|trans),
+        'form': form,
+        'back': path('admin_activity')
+    }) }}
+{% endblock %}