implement video controls on video-element

[GuidaGG]

• [x] add icon to play/pause
• [x] add mute icons and functioniltz
• [x] add icont to play/pause on mobile also on design page

[ah-bas-und-aer]

On the Researchpage the video should be muted when loading for the first time.

[GuidaGG]

ok!