PID tuning started

Started tinkering with PID values on the actual system (not in the simulation). Seems like sensor noise will make it difficult to use derivative term. Right now motor control in Drive is isolated to front left & rear right motors.

Also, testing done today made me realize there needs to be better handling of exceptions. Exceptions are just propogated to the top and then the motors are stopped. But exceptions were happening today just while ioctl'ing some I2C messages.

So, need to examine why Accelerometer is throwing exceptions during I2C transaction (discovered today) and also implement some safe exception handling in Drive so that failures like this don't cause the quadcopter to go crashing.