This commit adds a message to the Course Admin page when there are upgrades available for WeBWorK.

-  It checks for upgrades for WeBWorK and PG
-  It checks to see if your OPL database is out of date
-  It can be configured to use any set up of remotes/branches.
Bugtesting Commit
Made commit comparing a little more reobust.
another bugtest commit
Reverting bugtest
bugtest
Merge remote-tracking branch 'origin/upgrade-notifier' into upgrade-notifier
Refactored how git checks for being up to date.
Update README
Merge branch 'upgrade-notifier' of https://github.com/goehle/webwork2 into upgrade-notifier
Cleaning up unintended changes and getting support for math3.
Revert bugtest
Revert bugtest
Merge branch 'upgrade-notifier' of https://github.com/goehle/webwork2 into upgrade-notifier
Added ability to turn off system by setting any of the remote/branch variables to be empty

Added check to see if there is a new version tag and update the message
bugtest
revert bugtest
Check is a little slow so I made it only visible on the index course admin page.
Merge branch 'upgrade-notifier' of https://github.com/goehle/webwork2 into upgrade-notifier
Message appears on every page but is only checked once per day.