refs #222 - Minor PEP8 changes and other compulsions

Conflicts:

	rapidsms/contrib/messaging/urls.py
refs #222 - Docs for rapidsms.contrib.messaging
Added empty models file for rapidsms.contrib.handlers
``coverage html`` would not run without it.
refs #222 - Tests and bugfixes for rapidsms.contrib.messaging
Listed django-selectable on README
Typo fixes
Thanks @dpoirier!
Fix url template tag reference.
Style clean up.
Merge branch 'release-0.12.0' of https://github.com/rapidsms/rapidsms into release-0.12.0
Merge branch 'release-0.12.0' of https://github.com/rapidsms/rapidsms into release-0.12.0
Remove region tag. Update layout.html to check for existence of contrib.export.
Merge pull request #279 from caktus/feature/messaging-update

refs #222 - Tests and docs for rapidsms.contrib.messaging
Refs #269: Merge remote-tracking branch 'remotes/origin/release-0.12.0' into feature/269-footer-at-bottom

Conflicts:
	rapidsms/templates/layout.html

Branch: feature/269-footer-at-bottom