Users should download products etc via mirrors

All download links we provide should use links that support mirror sites and download statistics. See https://wiki.eclipse.org/IT_Infrastructure_Doc#Use_mirror_sites.2Fsee_which_mirrors_are_mirroring_my_files.3F and https://wiki.eclipse.org/IT_Infrastructure_Doc#See_download_statistics.3F.

There are already some other issues:

• We aim to address this for the website home/landing pages as part of #35 (closed).
• See also #53 (closed) for enabling download statistics in general.

For this issue:

• We should also check all other places (e.g. CONTRIBUTING.asciidoc etc) where we link to download.eclipse.org.
• We may want to put a custom HTML page on the downloads page. Currently https://download.eclipse.org/escet/ indicates: "This page is not designed to be web-accessible, as the project has not created a web page here. [...]". This seems to suggest that is possible. We could then provide friendlier download links (with hashes as per #86 (closed)), URLs for the update site, links to the installation instructions, link the website/documentation, etc. It would be great to still be able to browse the raw directory content as it is now, especially for us as developers (and to allow archiving files).

Currently downloads page for Eclipse ESCET: