Auto-generate date validity checks for all date DB Columns that are not NOT NULL (was missing so far).
Fix issues in the Partner Edit screen -> Personnel Data -> Application Tabs that prevented data validation from working correctly (it was not working / not working as intented - independent of the date control validation that I fixed/implemented in my previous commit!). 
(Functional changes to the data validation on those Tabs were done after discussing with WolfgangB how to go about the problems encountered.)
UpdateExtractChangeSubscriptionDialog: 
* Fixes regarding Date Checks. 
* Further fixes for more checks that were either not quite done like in the corresponding 4GL screen, or were missing altogether.

UC_PartnerSubscriptions.cs: None of the logic contained in that class was used anymore; it was a remnant of Petra 2.3's Subscriptions UserControl which worked rather different than the UserControl in OpenPetra. I emptied the Class, but placed a new shared Method for checking of the validity of the selected Publication in a ComboBox. That check is needed both in the Partner Edit Screen's Subscriptions Tab and in the UpdateExtractChangeSubscriptionDialog.

Template window.cs: Added the missing option to process Data Validation errors without displaying them.
Removed invalid and wrong XML comment.
merge from trunk
uncrustify
merge from branch 'lp:~christian-k/openpetraorg/dev_0002113_nullable_date_controls_validation'