add ofGetCurrentMatrix

* adds getCurrentMatrix to ofBaseRenderer and all its direct heirs

* adds ofGetCurrentMatrix which will return the current matrix state

* this will, in order not to over-optimise the code, return an ofMatrix4x4 by copy instead of a const ofMatrix4x4 & - I trust modern compilers will automatically move these things and find the code easier to optimise this way anyway.

Signed-off-by: tgfrerer <tim@poniesandlight.co.uk>