Slice: generate interface files in build/interface/cpp//interface/... instead...

Slice: generate interface files in build/interface/cpp//interface/... instead of build/interface/cpp//interface/cpp/... and adjust source files

git-svn-id: https://svn.sfb588.uni-karlsruhe.de/svn/HumanoidRobotAPI@18 e7ad446d-f7d8-486a-9efb-df2f5bbea5c6