Add 'theater mode'

[alukach]

To facilitate #130, it would be nice to have a theater mode GET parameter to show only the map portion of DC. This would really shine once #209 comes into effect. This way, I could embed my DC project into my blog and only show the product of the spatial operations. Might be nice to have a small link to the DC project available as an icon, something like "Edit in DropChop". See the CodePen example:

[mapsam]

👍 this seems cool - feel free to start chopping away at it!