This is the preparation of an attempt to make these tests work with
both a local github mock (in-memory) and a remote actual github.
Move a bunch of fixtures relying on the specific github
implementation (and odoo-as-library access) to the "local" plugin,
including splitting the "repo" fixture.
The specific fixtures will likely have to be adjusted as the
remote endpoint is fleshed out.
Reviews are interpreted like comments and can contain any number of
commands, with the difference that APPROVED and REQUEST_CHANGES are
interpreted as (respectively) r+ and r- prefixes.
