Add command to modify trust database

[steinybot]

Modifying the trust database is not as straight forward as it should be.

Something that should work but doesn't is:

gpg --batch --yes --status-fd 1 --command-file /root/.gnupg/commands --edit-key DE29CBE0AC9B2EB810E694D7B6A8B64B909CAF2F

With /root/.gnupg/commands:

trust
5

It seems to process the command file but it doesn't actually modify anything.

I think we will need to first export the trust database, then append new trust entries, and then import the new file.

This has to be done after #1 and #2.