Minimized mode for the IFrame API

The proposal here is to add a different “mode” to the IFrame API that enables the concept of “minimized” or “thumbnail” that allows you to have a expanded version, taking a big part of the screen, and the posibility of minimize it.

Example from the mattermost jitsi integration:

This can be partly covered by a “responsive” implementation, but It is not the same feature, because a responsive approach would need to cover way more interface than the proposed here, and at the same time you can’t make assumptions like “the user have a expanded view with all the features”, so in responsive you have to try to cover as much features as you can. In a minimized mode, you can focus in the specific use case of a restricted small view of the app.

I already have a proof of concept here: https://github.com/jitsi/jitsi-meet/pull/6932

The main parts there are: removing everything that is not essential (chat/filmstrip/some buttons), reduce the size of the watermark and the icons, and remove the selectors for the video/audio input.

I still need to improve the notifications look and feel and other interface parts like the popup forms.