NACK support

[cyphar]

Currently we only support two states:

1. Not accepted, where not enough LGTMs have been received.
2. Accepted, where >n LGTMs have been received and it's good to merge.

I think we should consider having another state:

• Rejected or NACK'd, where a maintainer has said "No" to a change. Now, this will be a bit tricky to make configurable (purely because of how hard it is to specify what the maintainence politics of a project are in code) but there should be a way to make it so that a NACK can't be overlooked by a maintainer.

WDYT?

[tboerger]

Makes sense, I also like NACK for that per default

[bkcsoft]

Like the idea, can definitively see it being abused 😆