Prevent click and scroll underneath drawer

[vonwao]

Clicks on the grayed-out overlay generate click events in the component behind the drawer.

You can also scroll the content behind the drawer. (I think in most cases that's not desirable).

[kevinthecity]

Also would love to see this

[Redmega]

So this is fixed by #51, but introduces some hard coded styling to the body, which might interfere with the users' styling. I'm not satisfied by that approach but I'm not sure if a better alternative exists, so I may merge it regardless.

[Redmega]

also just realized this is a duplicate of #24, so closing and moving conversation there.