Moves the tracking of revisions to the DB instead of the filesystem

As discussed via email.  It was actually a pretty straight-forward and fairly clean addition overall...  

Note -->  I did NOT update the SQLite adapter however, although I suspect the MySQL adapter code probably will work in there as-is (haven't used SQLite in a while though TBH) but I didn't test it as that adapter was already not working off-the-shelf and I didn't want to combine the fix into this pull request.  Let me know if you'd like to me to make it work for that adapter too, though, and I can do so pretty quickly / easily.

LMK if any concerns or questions otherwise hopefully this will help others too!  :-)

From the commit message:
Makes using version control & deploy management systems a lot easier. Also allows you to run revisions out of order if desired as they are now tracked individually instead of 'up to'.  Implementation is in keeping with the DB adapter / interface paradigm.  Only includes adapter code for MySQL however as the SQLite adapter is not currently implementing the interface properly [master branch as of now]; the MySQL adapter code likely would work as-is though.