Just plainly linking all files is not possible as hash files contain
name of file they verify. For latest medkit this file name is of course
different so hash files for latest medkits were invalid.

To fix this, move of hash files generation was required. Now hash files
are generated in generate_medkits script. To be consistent also signing
was moved there.
This change makes generate_medkit script just plain medkit generator.
Output is single file. Deployment specific additional files are
generated by generate_medkits script instead.