use cv2 and remove service as it kept blocking execution

[bajo]

Tested on the robot.

• no longer freezes after a while
• needs export DISPLAY:0 to be set
• somewhere eog is still called. needs to be found and removed (launchfile?)

[ipa-nhg]

@bajo probably you have some autostart jobs, check in .config/autostart

[bajo]

@ipa-nhg Thank you. I will check that.