Add: News post for 1.10.1 (OpenTTD#156)

Add: News post for 1.10.0 (OpenTTD#155)

Co-authored-by: Patric Stout <truebrain@openttd.org>

Fix: some more pixelated thumbnail images (OpenTTD#154)

Those of Jan 2020 were, like the previous commit, downscaled with the closest neighbour
algorithm. This now fixes that issue.

Add: screenshots from AlexTheDacian and ColdIce (OpenTTD#152)

Add: opengfx-nightlies is now available as binaries too (OpenTTD#151)

Fix: redirect non-latest releases to the CDN directly (OpenTTD#150)

As we no longer publish non-latest on the website, send them to
somewhere where the files are still available.

Add: 1.10.0-RC1 release announcement

Add: switch to cdn.openttd.org for all downloads

Here also is a file called "latest.yaml", which greatly simplifies
the "fetch-downloads.py". Additionally, as cdn.openttd.org is
browseable, we only need to serve "latest" (and no longer older
releases).

While at it, refactored fetch_downloads a bit to be a Python
module and run flake8/black on it.

Fix: [Actions] make explicit that we only want to checkout submodules

This is a change in defaults for openttd/actions/checkout.

Add: badges about the current deployment state of staging/production