Advanced arrays and documentation

[mjendruk]

Hi!

This pull request adds and changes the following:

• every supported type can be an array
• arrays are expandable in gui
• introduce AbstractPropertyCollection
• add docs
• introduce ensureGroup() method
• refactor PropertyGroup
• property constructor expect a pointer rather than a reference (see 720e83e323bf14ffdc036667c71f04189a47671e)

Attention Do not just merge. Please try atleast to compile and have a look at the doxygen generated documentation.