Use postgres notifications to listen to version updates.

You can listen to updates in the tests client like this:

python tests/tests.py http://localhost:8211 webboxebbox --box wsbox4 listen

It will push the new version number to you when an update or delete has
completed:

Listening...
Version updated to: 1
Version updated to: 2
Version updated to: 3

Requires new function in database.

Also cleaned up some use of str() to format()