Look for version number and display in admin interface if available

[leonardr]

As we're packaging the circulation manager as a Docker instance, we should be able to run git describe --tags and put the current version and revision into a file or the database. The circulation manager should then be able to pull the revision number from file/database and display it to admins (and possibly anyone interested).

This will help libraries who are paying for hosted service keep track of which version they're on.

Other techniques for packaging the circulation manager can do something similar -- all that matters is that the data end up in the right place.