needs frontend bits

- fix up filters
- fix missing icons bug
- fix missing close button

Can't use sh.tangled.repo.pull.state.{open,closed,merged} since
that results in a stateopen.go -- overwriting issue.state.open etc.
Hence, it's pull.status.

/:did/:repo/merge is only ever used when actually performing the merge,
so by this point all conflicts should've been rectified and the merge
*should* succeed. This is the appview's responsibility.

/:did/:repo/merge/check checks for mergeability, and can be used to
repeatedly check as the supplied patch is updated by the submitter.

- implemented in a backwards compatible way, introduces migrations and
updates an existing lexicon
- newly added field is not marked required, so we should still be able
to index old repo-create events properly

This should help alleviate the memory leakyness that was exhibited when
we stored the entire object.Commit in memory.

no cap

We're open to public!

we want to enable proper rollback mechanism on knots to eventually