Update to millipixels 0.17.0.

This forks Megapixels to Millipixels, because we agreed not to make a special effort to track upstream, and now Millipixels is more of a L5-specific project. Megapixels is still in Debian, so that warranted a name change to avoid packaging conflicts.

Based on https://source.puri.sm/Librem5/megapixels/-/merge_requests/52 and https://source.puri.sm/Librem5/megapixels/-/merge_requests/53

Draft because this needs to go in sync with https://source.puri.sm/Librem5/linux-next/-/merge_requests/430

Please review regardless of the draft status! It's there to prevent accidents with merging.

It can be installed alongside Megapixels, so there's no need to put off merging.