Rewrite TrogdirSyncinatorWorker

The Trogdir sync code has been rewritten to hopefully simplify it and
fix some of the bugs.

There are no known problems with this branch but additional testing may
be required before it can be used in production.

The "Update from Trogdir" functionality has been removed. I'm hopefuly
that the new code will be dependable enough that it won't be needed.

WCMS-352
Add TrogdirChangeWorker for concurrency

The TrogdirSyncinatorWorker will now kick off one TrogdirChangeWorker
per change which means the updates happen concurrently and finish much
more quickly.
Upgrade Rails to latest security release
Misc fixes for Trogdir syncing
Merge pull request #143 from biola/trogdir_change

Trogdir change