Option for accordion collapse mode in course

[henriasv]

When opening (uncollapsing) a course module, other modules collapse. The interface to the course author should be an optional entry "accordion": True in course.json

[danmichaelo]

Checked the bootstrap-vue docs. Adding the accordion behaviour in itself turns out to be just the matter of adding an attribute to the structure we already have. But as feared, it causes loss of scroll location and instant sea-sickness, so we need to fix #11 first.

[danmichaelo]

10 and #11 are a bit more intertwined than I first thought, so I'm closing #11. In itself, #11 can be easily solved with vue-scrollto, but it does not update the animation target during the animation, so combining them leads to overshooting:

To orchestrate the two animations we need more low-level control of them, which means some work.

Alternatively, one option could also be to drop animation altogether, or drop only the expand/collapse animation.