Tribler - first flatpak help

I created a working flatpak and plan to submit it to flathub in the future. Since this is my first flatpak I would be very grateful for some code checking, advice, mistakes pointed out, ect.

Here is the current state:

Project information:
Tribler is a research project of Delft University of Technology. Tribler was created in April 2005 as a new open source Peer-to-Peer file sharing program. During this time over one million users have installed it successfully and three generations of Ph.D. students tested their algorithms in the real world.
[from the tribler homepage]

Name: Tribler
License: GPL 3.0
Upstream has been contacted: not yet