Use tagger2 API for sqlitebuildtags.

At the time of this writing, tagger2 (the current version in production)
is missing a URL to export tags as sqlite like bodhi needs.  That
feature will be added back in soon.
Update pkgtags_url in app.cfg.
Merge pull request #1 from fedora-infra/feature/sqlitebuildtags-upgrade

Use tagger2 API for sqlitebuildtags.