Make it more generic by accepting any content except of just rows with text and
icons.

In addition, rework its structure so the animation is smoother, by putting the
background overlay outside of the Modal. This way, the animation doesn't affect
the background, which won't slide down.

It emulates Android's BottomSheet in pure JavaScript. It's implemented as
another Dialog, so it can be used instead of one.

The implementation only supports text options with an associated icon, and an
optional 'selected' marker.

left blank in default meet installations, to be overridden by adding <base href="CDN_URL"> to /base.html