In the past we used a PanResponder to detect user gestures in the sheet
to show a reduced version or a full-height version of it, and also to
close it.

There is an obvious conflic between the gestures and scrolling, which
didn't work all that great, but we could live with it.

After reactions were introduced we no longer rendered the 2 different
heights, so that functionaligy stopped being used but the PanResponder
still remained there.

This commit removes it completely and sets a max height of 75% on any
BottomSheet, so any tap outside will close it.