Support wayland

[alkisg]

Many issues must be solved before epoptes can properly support wayland.
The progress will be tracked here.

Thumbshots

• Currently epoptes-client > thumbshot.py crashes on wayland. Add a test -n "$WAYLAND_DISPLAY" as a quick workaround.
• A patch was merged recently in gnome to allow applications like epoptes to ask a permanent permission to take screenshots/thumbshots. Once it reaches the distributions, let's see if we can use it.

Monitoring / assistance

• Use the remote desktop xdg portals for this.