While at it, also remove unnecessary "#!/usr/bin/env python3" in files
that only get imported, and adjust other empty/comment lines in the
beginnings of the files for consistency.
This makes files easier to read, and makes the pmbootstrap codebase more
consistent with the build.postmarketos.org codebase.
It is dangerous to flash the boot partition on the Ouya. Doing so can
result in a bricked device. Allow deviceinfo to blacklist partitions from
ever being flashed.
* moved export code to pmb/export and split it up
* added deprecation notice to "pmbootstrap flasher export"
* made "pmbootstrap export" work
* adjusted the "pmbootstrap flasher export" hints in the code