Document Picture-in-Picture for browser meetings

Currently Jitsi uses traditional Picture in Picture in Electron application. Browser meetings support is not yet implemented. This idea proposes to implement Document Picture in Picture for browser meetings for supported browsers and traditional Picture in Picture otherwise. Document Picture in Picture mode allows to embed arbitrary HTML contents. The idea will be to use React's portal to create interactions buttons inside the Document PiP window that will share the redux state change. Interactions such as audio/video toggle, chat window will be added. Apart from that, different layouts such as compact, gallery, speaker will also be available inside the window.