[PATCH] models: Resolve issues with Patch.state

[Finucane, Stephen]

> The initial migration introduced in '30bb271' was incomplete: running
> 'makemigrations' on the current codebase will produce a migration which
> could not be applied cleanly. The reason for this was the non-loading
> of initial data for the 'State' model.
> 
> Fix this issue by only referencing the contents of the 'State' model
> when we have to (on save of a 'Patch' object), thus allowing the user
> suitable time to apply this initial data.
> 
> Signed-off-by: Stephen Finucane <stephen.finucane at intel.com>

Damien: are you happy for me to get this merged? I'm calling dibs on this issue unless you've a good reason to go with the other solution? :)

Stephen