Fix #154

Reduce the pressure on the tunnel.

If not the URL is encoded in UPPER CASE which is correct but looks
weird.

Need to define the address of the tunnel using KARAPULSE_TUNNEL_URL env
variable for now.

- use a bin as playbin video-filter
- use testbin to generate the background instead of using a static image
- move IP overlay to the bottom
- always display the IP and QR code overlays

Ensure the window sized is passed, fixing textoverlay scaling.

Fix #142

They take a lot of time to save and restore so slow things down rather
than speed them up.