Big changes to the rule class means that a lot of our methods were
wrong. Some of these (such as add) may not come back. In the new schema
it doesn't make sense to add rules together as you are going to be
talking about declarations instead.

However, one serious side effect of this is that the code for loading
and saving CSS from the database is completely broken. In order to fix
this I must first stabilise the API for the CSS values. Yay :/