write buildserver status as public JSON files

Building upon @uniqx's valuable build log support in !515 (merged), this now generates a JSON file to publish the status of any given command run on the buildserver. If the machine where it is running is configured with deploy_process_logs = True and setup to rsync, then this will also publish a running.json at the start of the process so we can tell which stage the buildserver is currently running. At the end of the process, it will publish a JSON file based on the subcommand name, e.g. fdroid update will publish update.json. These will all go into https://f-droid.org/repo/status/. This will also publish JSON files for the offline commands like gpgsign, but those will come only when the index is published.

This replaces the wiki pages, like https://f-droid.org/wiki/page/update, which we currently use for buildserver status. I think I have gotten all the required data out there. Then using this data, this information can be published in nice ways on the website, and wherever else people want to use it.

There are two other unrelated commits that were already tangled up in this work, so I left them in. They are fdroid import improvements as a follow up from !714 (merged).

@relan @Bubu @uniqx @IzzySoft @CiaranG @Rudloff @licaon-kter