mobile support

[freeman-lab]

There's at least one issue with viewing the control panel on iOS/android. This issue can be a place to track it, as well as any others that we find.

• range slider doesn't work because it's not supported on iOS, we should be able to use multirange instead (thanks @dfcreative for the tip!)

[rreusser]

I can try to take a stab at this. The range slider code could definitely be better, but its purpose is pretty focused and limited in scope, so can probably add some touch behavior and call it a day (vs. pulling in a dependency? no strong feelings either way, though I feel like most of the work with dependencies will probably go toward unstyling what the library styles).

[marcofugaro]

Range inputs are now supported everywhere, can this be closed?