Add "Use pager" to Views blocks to completely disable pager

In Panopoly 1.x, we had a "Use pager" checkbox to completely disable a View's pager. However, in Panopoly 2.x, we don't have an exactly equivalent option. There is "Pager type", but that only allows changing the type of the pager - you can't completely remove it.

I've struggled to replicate some widgets from Panopoly 1.x, so I think we need to add this back!