Notifications: Cleaned up mails, added debounce for updates

- Updated mail notification design to be a bit prettier, and extracted
  text to new lang file for translation.
- Added debounce logic for page update notifications.
- Fixed watch options not being filtered to current user.

lang/en/notifications.php

@@ -0,0 +1,26 @@
+<?php
+/**
+ * Text used for activity-based notifications.
+ */
+return [
+
+    'new_comment_subject' => 'New comment on page: :pageName',
+    'new_comment_intro' => 'A user has commented on a page in :appName:',
+    'new_page_subject' => 'New page: :pageName',
+    'new_page_intro' => 'A new page has been created in :appName:',
+    'updated_page_subject' => 'Updated page: :pageName',
+    'updated_page_intro' => 'A page has been updated in :appName:',
+    'updated_page_debounce' => 'To prevent a mass of notifications, for a while you won\'t be sent notifications for further edits to this page by the same editor.',
+
+    'detail_page_name' => 'Page Name:',
+    'detail_commenter' => 'Commenter:',
+    'detail_comment' => 'Comment:',
+    'detail_created_by' => 'Created By:',
+    'detail_updated_by' => 'Updated By:',
+
+    'action_view_comment' => 'View Comment',
+    'action_view_page' => 'View Page',
+
+    'footer_reason' => 'This notification was sent to you because :link cover this type of activity for this item.',
+    'footer_reason_link' => 'your notification preferences',
+];