Editing and deleting individual shipments

Enables editing and deleting individual shipments. There's an issue in that sometimes upon load ember data tries to request some associations (terms, sources etc) which it doesn't need to access, as they should already be loaded in respective controllers. I decided I'm not working around this issue roght now, because it seems that changes in Ember Data 1.0.0.beta versions should give us more control over loading, so I'd rather upgrade first (which is not straightforward, as there are breaking changes all over the place).