Orbit: bullets: explicit click handler

Add an explicit click handler to bullets. Previously it was handled
implicitly only with `settings.next_on_click`.
Orbit: next_on_click: only for slides

Narrow down the selector for the `next_on_click` handler to only match
the slides, but not the bullets.
Merge pull request #4949 from blueyed/orbit-fix-bullet-links

Orbit: fix bullet links (especially for `next_on_click: false`)