Add my KeePassX (0.4.x-svn) retina fork

There's basically two versions of KeePassX:
* New: version 2 alpha for which there's already a cask.
* Old: version 0.4.3 (plus some svn code - approx 3 years old - for which there's no official build yet). The official repo has been "closed" with a reference to the new client.

I've forked the old repo, added some retina glue and produced a binary that works with retina screens. The old 0.4.3 build looks excessively blurry on a rMBP.