Added MPU6050 class to lib4774 namespace.

This allows the files from the Arduino version of the library to remain untouched
in their own subdirectory, and means the class name of 'MPU6050' can be
used without clashes.
Left shift device address to account for 8-bit requirement of WPILib I2C.
Don't try to implement reading words in I2Cdev - just fail.