Fixes for CollisionGroups and CollisionLayers

This pull request should fix all issues in #180

- setCollisionLayers TorqueScript method now works properly with individual element input (n1, n2, n3, ...)
- directly assigning space separated strings to CollisionGroups and CollisionLayers fields in TorqueScript now works properly
- Taml now outputs both fields as space separated strings instead of a bit mask integer
- added Utility functions in C++ to convert between a string and bit mask (and back)