NEW UX: Let me hide the "Drag here to add more cards" areas

In Classic there's a "Preview Mode" that you can still build in without having to completely leave a dashboard's edit mode.  Even better the "edit mode" in classic basically IS the same view as preview, just with some dotted lines an the sort.  

In New UX, the edit mode adds a full page wide "Drag here to add more cards" zone between every new row of cards, each zone adding about 40 pixels in height that's not really there when you leave publish.  This expands the edit view and distorts what the page will actually look like when published.  

The "Drag here to add more cards" zones are fine as brand new builder to get the point across early on, but after about the 2nd or 3rd time a builder likely understands what to do and may want to turn them off to see a closer representation as to how things actually look when they're editing. 

The builder should still be able to just drag new cards between existing cards for the same effect, with or without these zones visible.