API 3.1 compatibility: Static configurable properties must be private and immutable.
Static configurable properties (db, has_one, etc) are now private. See: http://doc.silverstripe.org/framework/en/3.1/changelogs/3.1.0#static-properties-are-immutable-and-private-you-must-use-config-api
Merge pull request #16 from tractorcow/3.1-static-update

API 3.1 compatibility: Static configurable properties must be private and immutable.