#284

- changed heigth of the stichtagchooser dialog
- set lower bound for datepicker
- use bundle for error message texts
changed message for future stichtag message #284
popup downloadmanager dialog #284
 #284 use credential aware http download to retrieve product
#284 changed error messages
close #284 dont allow manual edits in stichtag chooser
Merge branch 'feature/284-improvements-stichtagbezogener-bestandsnachweise' into dev