Add application 'builds' for CI jobs and build results

[txels]

Following on the previous PR's footsteps, these are additional models for a builds app.

I think it's important that we get the data model right to begin with, then we can start building the providers and the front-end based on that.

Next step, a features app.

[txels]

I got rid of the Job model, not really needed here. Added data in the build that the provider can use to retrieve job information etc.