bulma (call): add a button for screen sharing: - add a button for screen sharing, only on desktop - split `muted` state to `inactive` and `muted` where `muted` is only about the color - use the `inactive` state with an other color (in `screen-off` class) to indicate when screen is not shared rel 432

<div id="list" class="container has-background-white px-1 py-1">
    {% include "list/view_generic.html" %}
</div>