[REFACTOR] moved externalized messages

Moved messages from de.*.dpp.project.Messages (who created this ?!) to
de.*.dpp.ui.Messages !

Change-Id: I27aa11776647aa0cebe6d73fa633ac056e6c54c9
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1146
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>