Appdata related improvements

Use translate tag in metainfo files

Appstream project no longer supports translatable=no properties

Source: https://github.com/ximion/appstream/issues/623

Add vcs-browser and translate URLs

At minimum url type="homepage" tag must be present to pass validation but it is best to include other links too.

Source: https://docs.flathub.org/docs/for-app-authors/metainfo-guidelines/#url

Add branding colors

Applications should set a brand color in both light and dark variants. This is used by Flathub and native app store clients on banners, app pages, etc.

Source: https://docs.flathub.org/docs/for-app-authors/metainfo-guidelines/#brand-color