Blender Git Loki

Refactor: Use more general appraoch to get data from BCMatrix

Added virtual function get_value_for() that can pick the correct data
from a Matrix (and later also for a vector or a float array) (wip)

this is in preparation for adding Sample data for Materials, light and camera
Those animations do not need matrix values, but either simple float arrays
or float vector arrays. I still want to handle those animation samples
in the same way as the Matrix samples. So i try to use a class hierarchy here
with the base class BCSample and derived classes where BCMatrix is the only
implemented subclass so far. (wip)