Provide and use functions for logging

This makes success, info, warning and error logging consitent and colourful.
Build YUM repositories during release

1. Collect RPMs.
2. Sign RPMs.
3. Create repository metadata.
4. Sign repository metadata.

This allows us to have signed released without leaking GPG keys to our repository server.
Unfortunately `rpmsign` doesn't support `gpg-agent` so the passphrase must be re-entered.
Merge branch 'logging-and-packaging' into fix-git-invocations

Conflicts:
	src/releasing/releaser.sh