IMPROVE: Allow clicking on whole admonition title

[rkdarst]

• This was inspired by the discussion in Improve toggle button design and structure #28, and having a bit of
  spare time and wanting to try something. This gets the "admonition"
  part of those design ideas.

• In the javascript setup, also configure the whole admonition title
  element to be clickable. This happens only in the case where it is
  a direct descendent of the admonition box and there is only one
  admonition title descendent.

• This is not designed to be perfect, but is designed to be mostly
  safe with most themes. It still could cause problems, but it has
  been tested with alabaster, sphinx_book_theme, and sphinx_rtd_theme.

• I don't claim to know javascript or CSS, or have deep knowledge of
  sphinx-togglebutton. But I do know enough and could read and web
  search enough to see how to add the onclick watcher + data to
  identify the right thing to toggle.

• Suggested reviews:

  • Someone that knows sphinx-togglebutton should see if this makes
    sense.
  • Someone that knows javascript should see if this makes sense
  • It would be prudent for someone else to test (I've tested the
    three themes above and firefox/chrome)
  • But if no one can test the above, it seems fairly safe to me and
    could be released and fixed later.

[rkdarst]

Just wondering if this was noticed (I submitted it during the holiday times)

[choldgraf]

Ooh I did miss this! But I think that it's a nice addition! Ideally we could do this purely with CSS, but I think adding the JS functionality is a nice step forward nonetheless.

I added a quick additional CSS rule so that the mouse becomes a "pointer" when you hover over toggle-able admonition titles, but other than that this seems good to go. I also removed some specific selectors for div so that this works with newer versions of sphinx/docuils

[choldgraf]

Let me know if my commits look good to you @rkdarst - then we can merge 👍

[choldgraf]

many thanks for this improvement @rkdarst !