Just make an AppImage

Just call just-make-an-appimage.sh to:

1. build a Docker image containing craft and some dependencies of the ownCloud client
2. run craft-appimage.sh in a container to build the client using the image we just built

Once it's finished, you should see a nice up-to-date AppImage in your current working directory.

Stuff that works

• AppImage passes quality checks like appimagelint
• AppImage runs on major distros, including xubuntu 18.04, Debian 10.8 with LXQt, Linux Mint 20.1 with MATE, Fedora Workstation Live 33, openSUSE Tumbleweed KDE Live Snapshot 2021-03-07

Stuff that doesn't work yet

• AppImages lack version numbers
• AppImageUpdate