Add ability to log use of assistance

When the user logs that they take the dose they should also be able to add if they ahve been using some sort of assistance.
There should ALSO be a seperate standalone log for whenever the user takes an assistance unit.

Start by tracing the existing dose-logging flow and how logged doses are represented. Define how assistance is recorded alongside a dose and how a standalone assistance entry is created; the work is done when both actions can be logged and displayed consistently.

Written by the indexing model from the issue text.