Added state representing "no network service available" case.
Implemeneted disabling network service on demand
Extended and refactored disabling of unconfigureable items.
Fixed disabling items in routing dialog
Updated changelog
Removed useless code

disabling of buttons according selected service was handled at place
where no change in service could occure.
Added comment
Merge pull request #210 from mchf/bnc878719

Handle disabled network service