Fixed bug in BrickPiUpdateValues: Temp_ENC_DIR not defined

Fixed bug in BrickPiUpdateValues: Temp_ENC_DIR not defined when changing motor encoder with positive offset. 
Replaced tabs with spaces.

Added initial version of thread safe python interface to BrickPi. Please have a look at ThreadSafeBrickPi.py, LEGO-Sensors.py and the examples.
Currently only Lego sensors have been implemented. MindSensors AbsoluteIMU will follow later.
I'm also working on implementations for Dexter Industries sensors based on the given examples. However, because I don't have those available I cannot test if the implementation is correct.