Provides a less manual interface for creating the freeze:
* takes the name of the branch to create
* takes any number of PRs which must be part of the freeze
* takes PRs representing the HEADs of the new branches
Then essentially takes care of the test.
Implementation of the actual wizard is not trivial but fairly
straightforward and linear, biggest issue is not being able to
`project_id.branch_ids[1]` to get the new branch, not sure why but it
seems to ignore the ordering, clearing the cache doens't fix it.
When creating the branches, add a sleep after each one for secondary
rate limiting purposes. Same when deleting branches.
Also the forwardbot has been updated to disable the forwardport cron
while a freeze is ongoing, this simplifies the freezing process.
Note: after recommendation of @aab-odoo, tried using `_applyChanges`
in `_checkState` but it simply did not work: the two relational fields
got completely frozen and were impossible to update, which is less
than ideal. Oh well, hopefully it works well enough like this for now.
To prep for the addition of the freeze wizard:
* move projects out of `pull_requests.py`
* then realize half the methods there have no relation to projects and
move them to more relevant places in `pull_requests.py`
* update corresponding crons (and tests using those crons) as the
methods have changed model, and the cron definitions thus need to be
updated
* split update to labels out of sending feedback comments while at it:
labels are not used much during tests so their manipulation can be
avoided; and labels are not as urgent as feedback so the crons can
be quite a bit slower
* move the project view out of `mergebot.xml` as well
