Keep posted form data

Whenever errors are found during a save by the table object and the savestate option is set FOF stores the data in the session. However when a form has serverside validation and an error is found, the data is not stored in the ssession. This leads to loss of already filled in form data. My proposal is to also store the posted data in the session whenever a server side validation fails. To me this makes the behavior consistent.
Merge pull request #285 from roland-d/patch-3

Keep posted form data
Update form/field/usergroup.php

Delete the commented out section in the getRepeatable() method that is confirmed not applicable to this FOFFormFieldUsergroup class. This is a housekeeping commit as the there is no net effect on what the code does. Also effected is form/header/usergroup.php, which will be deleted.
Delete form/header/usergroup.php.

Delete this file as it is not called by /form/file/usergroup.php::getRepeatable(). This is a housekeeping commit as there is no net effect on what the code does.
Handle empty and default calendar values
Merge pull request #289 from roland-d/calendarDefault

Handle empty and default calendar values
Merge pull request #288 from bbloom/fixusergroupfield

Fixusergroupfield
Close #290
Merge pull request #292 from akeeba/feature/290-update-transparent-auth

Close #290
Close gh-296