Add approved field on models with default False

Should be used to filter what projects are allowed to build during the
beta phase.
Add support for bootstrap alerts from dj messages
Add info alert when there is an unapproved project
Make view tests support django messages

Storage backend for the messages needs to be set when using RequestFactory
Merge pull request #73 from frigg/approved-field

Add approved field on models with default False
Merge branch 'master' of github.com:frigg/frigg into build-workers

Conflicts:
	frigg/builds/models.py