Implement custom dependency resolver

[hwittenborn]

As time is going on, it's becoming more apparent that Tap should be resolving dependencies on it's own, using a custom resolver.

As of current Tap already somewhat has to use a custom resolver built on top of the one built into the Python APT library, as things like dependencies and conflicts for MPR packages have to be manually checked and verified, so Tap should just go all-out and go from scratch.

This will also add some other benefits, such as allowing for MPR dependency support, which would be highly beneficial to Tap for mainline usage.

Would close #34.