Support for offline provisioning of apt-packages by caching `/var/lib/apt/lists` [GH-84]
:warning: Massive refactoring of buckets code :warning:

Doing this is kinda irresponsible because we don't have any unit testing
in place but I've had enough of copy & pasting things around. Although it
doesn't make the codebase GREAT, I believe it'll reach a _nice_ status :)

Thanks to those changes I realized that skipping configuration of
buckets that have already been configured was easier than I thought and
should be enough to close GH-85 \o/