Approval workflow

[Briehan Lombaard]

It might be worth breaking this into smaller features (or tasks), but we need to start working on the approval workflow documented in the specification document.

Right now a potential observer can save a proposal as a draft and that's basically it. In addition to this they need to be able to submit the proposal at which point the proposal state changes to "submitted". This should essentially make the proposal "read-only" for the observer from then on except for changing the state to "declined" from "allocated" when they are not happy with the slot that they've been allocated.

For the time being, we can then test the rest of the process from the Django admin. We'll probably end up building an administrative interface for the people responsible for the other steps in the process.