Hot swap button optionally visible by port

We need this for elm-debugger so on /edit/ we don't show the hot swap button.

Style notes? (line +162) I'm iffy on that line's indent...it is 4 spaces though.
I think `hotswapButton permitHotswap` should come down a line. This would hit the "if it can't fit on one line, it needs to have a newline and four spaces" rule. Need to write this stuff down so badly! :P