Use a Long id again because dates are hard to bind

When using forms, dates are hard to bind
Remove database filling

Using the Global class is much more flexible, especially when there are
schema changes
Add findByDate method to turn a Date into a Dag
Add test for Dag.findByDate() method
Import aanwezigheden from csv file
Return null when dag is not set for toString
Add findById method to get a Dag by id
Add a method to register attendances for a Kind

This method I'm not happy with, it should be possible to do it more
elegantly. Binding the form did not seem to work for some reason.
Add route to save attendances
Made a form so it can be submitted

Also added hidden fields so it can be bound
Add method to register a morning attendance

No more two lines when registering an attendance
Use new registerVMAttendance method everywhere