ArduCopter: reduce redundant event logging

We now only write state changes to the dataflash log when they have
changed.
Also replaced <tab> with <space> in AP_State.pde
ArduCopter: fixed minor bug in logging of parameter changes to dataflash

It is questionable whether we should even bother writing these to the
dataflash as there is no way to recognise which parameter has been
affectded
ArduCopter: use new logging method for remaining packet types

Additional changes include renaming RAW dataflash type to IMU