Respect user-selected data directory location

[GeoS-gh]

MakeMKV flatpak fails to respect user preference for data directory location.

Steps to reproduce:

1. Open MakeMKV preferences
2. Set data directory to alternate path and close application
3. Re-open and find all preferences reset since app seeks data dir in /home/${USER}/.MakeMKV

Also, rather than defaulting to /home/${USER}/.MakeMKV, shouldn't the default location for the data directory be /home/${USER}/.var/app/com.makemkv.MakeMKV/.MakeMKV thereby more closely adhering to flatpak confinement conventions?