Include bootloader in firmware release images

[bessman]

The current release process automatically builds and attaches firmware images to the release page. These firmware images include only the application firmware, not the bootloader. If someone were to flash these images with a PICkit, the existing bootloader would be erased and the PSLab would no longer be able to enter bootloader mode.

It would be good to also build the bootloader and merge it into each of the release images, as documented here. Then the release images can be safely flashed with a PICkit.