bootloader and boardloader code reorganization

[TychoVrahe]

We currently have large part of boardloader and bootloader functionalities in main.c files.

This is sub optimal, as these have grown substantially and are hard to navigate and understand. Lets split this into more files with some logical grouping.

Bootloader could also use clean separation of communication code from firmware update code, state machines etc.

Bootloader_ci could also profit - we could perhaps reuse more code between the two targets and thus simplify maintenance.