Provide an official AppImage or Flatpak for Anki on Linux

[ferophila]

Request: .deb package for Chromebook users

There is an existing binary bundle available, and I’m stretched for time as it is. Even if someone were to come along and contribute a script to build a .deb file from the existing binary bundle, there’s no guarantee they’d stick around to deal with any problems that come up in the future, and then it becomes yet another thing I need to maintain.