Tests for proposal supports integration

[oliverbarnes]

Very WIP.

Looking to get a quick win through simple vcr-based system/acceptance tests. I've added a basic one for proposal supports that passes when running locally with the lv api running in parallel, without VCR wired in yet.

The next steps I had foreseen were:

• wire this initial spec with VCR
• write a similar spec for removing support
• then write similar specs for creating and removing delegations
• I'm expecting the last two steps will be quick because it'll be very similar to the first one.

And this will be good enough for this first PR. We'll have basic coverage for the happy paths

Closes #16

@davefrey I just saw you had assigned this to yourself, sorry about that. Let's coordinate if you're also working on it this weekend, else I'll just continue on it and we can have a look at it together on Monday

[davefrey]

Carry on, I'm happy you took it