Merge of all branches of Fabian PK (related to skills)

• Merge improved SkillManagerGUI from Tobias Bodmer
• Fix aron code generation for classes without members

@reister. YOu only need to review the changes to aron (Generator.cpp)

Depends on MR armarx-core!246 (merged)

Includes MR !285 (closed) and !320 (closed)