Overhaul `fdroid import`
This is a big overhaul of fdroid import to make it work a lot better. It also adds rudimentary support for react-native and flutter. Once we understand those better, I imagine we can improve fdroid import more. This is then used in the issuebot, which will be showing up soon on rfp and fdroiddata.
This also adds fdroid scanner --force to force scanning of disabled apps and builds. This is required in issuebot runs, since fdroid import makes disabled builds by default.