NOMM version 0.12.6

Another patch to get ever so closer to a Flathub release!

• Changed how portal permissions are handled. From now on users will no longer need to provide override permissions to their downloads and staging paths.
• Fixed a major performance bottleneck when opening the settings screen.

List of PRs

• Flatpak portal permissions enhancement by @Allexio in #110

Full Changelog: 0.12.5...0.12.6