Add a new config section "mirrors", to replace the mirrors_alpine and
mirrors_postmarketos options. This will allow for more flexibility since
we can then handle the systemd staging repo (and others like plasma
nightly) with relative ease.
The loading/saving is fixed and now properly avoids writing out default
values, this way if the defaults are changed the user won't be stuck
with old values in their pmbootstrap.cfg.
Signed-off-by: Caleb Connolly <caleb@postmarketos.org>
Keeping the Config class in types seemed kinda weird and was just done
as a workaround to some cyclical imports. But now things are more in
shape let's move it to core.
Signed-off-by: Caleb Connolly <caleb@postmarketos.org>