Give player health views mirror alignment.

Now, player 1's name and health number are on the left, while the damage
bar is right-aligned; player 2 is the reverse. This involved a mix of
CSS and CLJS, but it may be possible to get the effect entirely in CSS
later.
Indicate the selected player with boldface text; default p1 selected.

Also some comment improvements.
Update health-view.selected to health-view.current for consistency.

The active player should be called "current" instead of "selected", to
help indicate that damage is coming _from_ that player and affecting the
opponent. "Selected" is more ambiguous in its connotation.
Split damage buttons into their own Om component.

I had to pass the hit channels in as a component property; but still,
this seems like a wise refactor. I should probably try to make
components even smaller.