Detailed list of changes:
* Since the list of actions is now long, move it into
  an action box that is displayed only when applicable.
* Display help messages when hovering over action buttons.
* Hitting return in the search box invokes "focus" action.
* Cleaned up stale css entries.

I have attached one of the resulting pages to see what things look like easily.  It is static, so won't allow navigation to other pages, but should be interactive enough.

[benchcpu.zip](https://github.com/google/pprof/files/1151238/benchcpu.zip)