fix english translation keys

the translation key in the mail view is generated with

````ruby
link_to(t(:"text_#{@content_type}_for_meeting",
   ...
````

@content_type is a string, for example: "meeting_agenda"
The translation keys must be named accordingly

config/locales/en.yml

@@ -61,8 +61,8 @@ en:
   label_notify: "Send for review"
   label_version: "Version"
 
-  notice_timezone_missing: No time zone is set and %{zone} is assumed. To choose your time zone, please click here.
   notice_successful_notification: "Notification sent successfully"
+  notice_timezone_missing: No time zone is set and %{zone} is assumed. To choose your time zone, please click here.
 
   permission_create_meetings: "Create meetings"
   permission_edit_meetings: "Edit meetings"
@@ -76,9 +76,9 @@ en:
 
   project_module_meetings: "Meetings"
 
-  text_agenda_for_meeting: 'agenda for the meeting "%{meeting}"'
   text_in_hours: "in hours"
+  text_meeting_agenda_for_meeting: 'agenda for the meeting "%{meeting}"'
   text_meeting_agenda_open_are_you_sure: "Unsaved content in the minutes will be lost! Continue?"
-  text_minutes_for_meeting: 'minutes for the meeting "%{meeting}"'
+  text_meeting_minutes_for_meeting: 'minutes for the meeting "%{meeting}"'
   text_review_meeting_agenda: "%{author} has put the %{link} up for review."
   text_review_meeting_minutes: "%{author} has put the %{link} up for review."