Lower host permissions to home permissions

[NoTuxNoBux]

References #40.

[flathubbot]

🚧 Test build enqueued.

[flathubbot]

🚧 Started test build.

[flathubbot]

❌ Test build failed.

Help

• bot, build - Restart the test build
• bot, ping admins - Contact Flathub admins

[NoTuxNoBux]

Flathub linting won't even allow home any more, apparently. That leaves us with two choices:

1. Ask for an exception (possibly replacing host).
2. Add something else such as xdg-documents, but that forces users to either put their projects there or to add an exception using Flatseal or similar. Worse, a user can still select a broken path from the hub, i.e. there is no discovery for that.

I already tried having no permissions at all, and whilst the hub behaves correctly by setting the project folder to a path from /run/user as mapped by Flatpak, the Unity Editor refuses to open the path, claiming the 'project is already open in the editor' - this is with Unity 6.1 which is fairly recent; none of these likely support portals or these mapped paths properly.