Remove row expander target if no sub actions defined

fixes #4401
Fix CronkBuilder adding "CUSTOM-"-prefix everytime a cronk is saved

fixes #3917
Fix Json Filter in URLs

Now the filter isn'T encoded in the cr_base part of the cronk string, but appended
as a get parameter. This avoids issues with url parsing

fixes #4425
Merge branch 'next' of ssh://git.icinga.org/icinga-web into next