Crosshair component - dimensions should be optional

[jamesleesaunders]

Summary

Modify the crosshair component to also work as an axis.

Detail

Currently the crosshair dimensions default to 40,40,40 if no .dimensions() option is set. As well as working as a crosshair I have started also using this component as a basic axis (for example on the Vector Field chart). Therefore it would be good to modify the crosshair component to also accept axis options to calculate the dimensions (and make the dimensions() optional).

Relevant Files

/src/component/crosshair.js /src/component/axis.js