Set up flathub x-checker-data to automatically detect new versions

As of #35 we are using mostly git sources now.

the main blocker on this is https://github.com/flathub-infra/flatpak-external-data-checker/issues/252 (essentially the ability to rerun our scrupts to update the two json files with any dependencies that changed in the updated versions of the app

We also probably need a way to update the JustCef source in the dotcefnative module in sync with the main repo's justcef submodule