InterfaceAgent; Fix "Invalid ChallengeToken"

The merge of the Object Manager branch caused a regression that caused
"Invalid ChallengeToken" errors, because the LayoutObject's intiialization
code ran in ->new(), but the information wasn't available
Merge branch 'interfaceagent-initialize-layout' of github.com:moritz/otrs
Use ObjectManager to create language object. Avoid double LayoutObject instantiation.