moved over to use BBGun

xdom is now BBGun, and most of slate is moved over to use it.

This includes removing, or simplifying, a tonne of code in slate,
mostly in the touch-bar.

assertFun was changed to assertFunction,
and isObj changed to isObject.
move bugs found and fixed with BBGun, and the Touch integration.

A lot more internal checks have also been added.
fixed use of click events.