Election status part 2 - cancelled elections

[chris48s]

First bash at allowing us to deal with cancelled elections:

• Data model changes to allow us to store that an election is cancelled, attach a document or notice and link 2 election records when one replaces another
• Basic front-end work to allow an admin to set the 'cancelled' flag and 'replaces' field in /admin (front-end for notice document is TODO)
• API changes so that client apps can pick up cancelled elections (this can be safely deployed without making changes to API consumers)
• Front-end changes for showing cancelled elections on the EE website:

Next steps:

• Changes to consume this data in YNR, WCIVF, WDIV
• Front-end changes to enable a wider group of authenticated users to use some of the features added here and in the last few PRs

[chris48s]

Having added a couple of checks in here, it occurs to me that we've probably got various bits of validation in the wizard form class, ElectionBuilder class and /admin. When we add more front-end for authenticated users that problem will probably get even worse. I reckon it probably makes sense to try and collate more of that validation logic here in the model class, but I think I'll leave that to another PR to try and keep the scope of this one sensible.

[symroe]

Yep, this looks great! One small comment, but otherwise good 👍

[coveralls]

Coverage decreased (-0.05%) to 71.293% when pulling 60bd28d on chris48s:cancelled_elections into d12f455 on DemocracyClub:master.

[coveralls]

Coverage decreased (-0.05%) to 71.293% when pulling 60bd28d on chris48s:cancelled_elections into d12f455 on DemocracyClub:master.