[FIX] RegForm: validation for second session
[MIN] RegForm: None option for Social Events
[FIX] RegForm: 'Modify my registration' TPL
[ENH] RegForm: Implemented auto-fill

* File and date fields are still missing
[ENH] RegForm: Added validation error dialog
[REF] RegForm: Code cleanup

* Removed legacy javascript from TPLs
* Refactorized field API call
* Moved regform-wise dialogs to dialogs/ root folder
[FIX] RegForm: userdata handling

* Data received is different before creating a registration
[FIX] RegForm: accommodation dates validation

* Selecting departure date before arrival date is not possible anymore