sick notes, styling of form

refs #9469
sick notes, add char counter for comment textarea

refs #9469
sick notes, integrated datepicker

refs #9469
sick notes, implemented save functionality

* new sick notes can be added now
* added sick notes list for overview

refs #9469
sick note, added field work days, adjusted table

* table with sick note now having new fields:
** AU present
** last edited
** number of work days

refs #9469