This allows us to use different colours for different timers,
which will be useful when we add a pacing timer.

This will allow us to reuse the display code for displaying
an additional pacing timer.

When a slide has several fragments it could be convenient to define a note for each of them. In this case we need to show only this specific note defined in a fragment and not others. General note of a slide shouldn't be also shown, as a more specific one should have greater relevance in this case.

Closes #1392.

It would be nice if we could define a custom notes.html file.

Actually, I'm used to compile my js files before releasing my app and, using selectors like `script[src$="notes.js"]`, doesn't work :(

So, what do you think about it?

This prevents the upcoming slide on the notes page from triggering
slidechanged events.  I believe this fixes issue 578, as well.

Resolves an issue where the first label (e.g., first bullet or first
number) of a list would wrap to the right side of the window and be
hidden under the clock element.