Use new Freezable traits for freezing
Add unit tests for the implemented abstract methods from FreezableTrait
Lock to the stable version of clippings/freezable
Update to clippings/freezable 0.2 and use is_frozen columns
Remove dependency on freezable behavior

Until now the freezable behavior configuration was modified on the fly
to tell store purchase models which used the shippable store purchase behavior
to freeze the shipping association as well.

Users of the shipping module would need to do this by themselves usign the freezable traits
and their abstract methods.
Add branch alias for the next version
Merge pull request #5 from OpenBuildings/freezable

Use new Freezable traits for freezing