tests: Remove stray print call
models: Drop the Release.get_version method

This is a leftover from Bodhi 1, we now have an actual version attribute
for the Release.
models: Make the version a string

Some Bodhi deployment might really use versions like '13.10', so an
integer won't cut it.
tests: Add a version to the release int he test db

This is going to be useful to test listing updates by release.
Add a new validator for releases

This will be useful to list updates by release.
views: Allow filtering updates by release
tests: Check listing updates by releases