Add graphing to show the angle between the solar wind flow and dipole axis as a function of time

It would be quite useful to have an optional small graph (possibly using a library such as [chart.js](https://www.chartjs.org/docs/latest/) or [C3](https://c3js.org/)) showing the angle between the solar wind flow and dipole axis as a function of time (updating in realtime).

Start by locating the existing solar-wind flow and dipole-axis data and the realtime update path. Evaluate Chart.js or C3 for an optional graph of their angle over time, and confirm that the graph updates in realtime and can be omitted when disabled.

Written by the indexing model from the issue text.