Before this change, a CI override would have to be replicated on most
/ all forward-ports of the base PR. This was intentional to see how it
would shake out, the answer being that it's rather annoying.
Also add a `statuses_full` computed field on PRs for the aggregate
status: the existing `statuses` field is just a copy of the commit
statuses which I didn't remember I kept free of the overrides so the
commit statuses could be displayed "as-is" in the backend (the
overrides are displayed separately). And while at it fix the PR
dashboard to use that new field: that was basically the intention but
then I went on to use the "wrong" field hence #433.
Mebbe the UI part should be displayed using a computed M2M (?)
as a table or as tags instead? This m2m could indicate whether the
status is an override or an "intrinsic" status.
Also removed some dead code:
* leftover from the removed tagging feature (removed the tag
manipulation but forgot some of the setup / computations)
* unused local variables
* an empty skipped test case
Fixes#439.
Fixes#433.
