therapy_timeline: clearer meaning for dots/rectangles (OOF/REG)

[peterdutey]

This is about the visualisation of prescription on the therapy_timeline() htmlwidget.

Make it clearer the dots are one-off administrations whereas rectangle indicate regular prescriptions. Perhaps on tooltip

• [ ] make tooltip appear faster
• [ ] bigger dot and centered vertically like the rectangles
• [ ] review tooltip texts more generally
• [ ] draft a blurb on the vignette.