#115 - Update upgrader to match latest civix template
This goes along with !120 (merged) but have put it up separately.
The main change is to remove the self-handling of versions in Upgrader_Base::setCurrentRevision and then the rest is just bringing the file in line with current templates. Then also bringing the main php file in line with current, and the main change there is the postInstall which is what allows us to remove the self-handling in Base.