Remove a few balloon popups and show their text on the page instead.

At minimum, I want to remove Prototype JS and instead place a dependency on
JQuery (which means finding or making a new balloon library). However, the best
option would be to make the balloons unnecessary, as much as possible.

In practice, this means either:

- Copy the text of the balloon as helper text. That's what I did a few times in
  this commit. This works really well on form elements too.
- Simplify whatever the balloon is trying to explain, enough to make the balloon
  unnecessary.

Once the above is done in all places possible, it's reasonable to revisit if we
still need the balloon functionality at all. I still want to depend on JQuery
because it can come in handy in other places, but I can't easily do that until
we lose the dependency on Prototype JS.