Large redesign, due to the way couplings work. Subsystems are now integrated into Components, requiring less FreeCAD objects. Couplings will get a list of all Components that connect via them, as well as a list of all enabled paths.
Initial rewrite of Connections and Couplings. Functions added to detect connections and couplings. Support for cavities has been added.
Merge pull request #27 from FRidh/master

Redesign Connections and Couplings