Merge tag '2.0.3' into develop

2.0.3
Updated french language
Fix #280
Merge branch 'develop' of github.com:getkirby/panel into develop
Fix #277 - Empty Select Option even for required fields
Merge branch 'bugsysop-master' into develop
Fixed overwritten URL-Key after saving a form
URL encoding for files
Refactored js structure
Merge branch 'release/2.0.4'