Hodograph with configurable appearance

[chird]

• [x] Maximum wind speed
• [x] Labelling of each wind speed circle

[chird]

Is implemented. But there are some bugs, when the configuration is changed after the hodograph is plotted. Add tests.

[chird]

The circle labels should optionally have a unit prefix. And the unit of the label should be configurable.

[chird]

Probably the x- and y-axes should be plotted from edge to edge.

[chird]

Bug:

• [x] Font of circle labels couldn't be changed