firmware: Fix loophole in protocol

This fix prevents the host program from issuing page writes without
transferring data first.
firmware: Slow down AVRDUDE in makefile
firmware: Changed handling of OSCCAL calibration

If the calibrated OSCAL was saved during programming it will be reloaded
before starting the bootloader, regardless whether it was entered or
not. This allows calibrating devices without PLL to 12 MHz.
firmware: Upload configuration files for new OSCCAL