I set these as separate bits by mistake when there's no good reason for
them to be like that, as they are not flags that are meant to be combined,
but a list of exclusive values.
Implemented the following functions along with the required internal APIs:
* flatpak_installation_get_id ()
* flatpak_installation_get_display_name ()
* flatpak_installation_get_priority ()
* flatpak_installation_get_storage_type ()
It's meant to provide a list of the system installations, not
just the default one, which can still be obtained by calling
flatpak_installation_new_system(), as usual.
Provides access to the functionality offered by the new internal API
flatpak_dir_update_remote_configuration(), in a similar way to what
can be done via the command 'flatpak remote-modify --update-metadata'.