Refactor limiting number of video players on fronts

Doesn't really get rid of the nastiness so much as move it out of the template at least ... 

I think probably the nicer thing to do would be have classes representing item types at different breakpoints, and then have code that converts that into CSS classes. We could also then add additional metadata, such as whether a video player should be shown for that item at that breakpoint. 

However, I think that would make it more difficult to move quickly at this point, and raise the barrier of entry for people editing the slice config, which I don't think is the right thing to do.

Hence just moving the hackiness, rather than eliminating it.

CC @phamann