this moves out all the high level logic from ArduPlane/ArduCopter to
the library. It also adds a "config page", as the last page in the
flash. This is used to check if the flash needs erasing. We only erase
now if the DF_LOGGING_FORMAT has changed.
This patch also adds a public CardInserted() method, which is used to
disable logging on APM2 if a dataflash card is not inserted
this moves all the non-hardware specific code to the parent
DataFlash_Class class, keeping the hw specific code much smaller and
simpler.
This should prevent discrepancies creeping in between APM1 and APM2
support again
Andrew Tridgell