Switch from UUID primary key to UUID pseudo-primary

Due to all the problems with UUIDs in rails4 as a PK option, maintain
two keys - the easy integer key which we'll not expose, and an easier
UUID secondary key.
revert to mainline rails

Now that we're not using the (broken) UUID as PK support in rails4
we no longer need the fixes from git.

Revert to the gem to make maintenance and deployment easier.