Support new GPlates continuously deforming plates

[davenquinn]

Gurnis et al, 2018 outlines a new method, implemented in GPlates v2.1, for modeling continuously deforming plates. This is excellent news for continental and continental-margin tectonics in particular. As more plate models begin to incorporate the ability to model plate internal deformation, it would potentially be useful to model this in Corelle.

This transformation is mathematically more complex than the finite rotations employed in the current iteration of the model and will be much less performant for client-side rotations, so this is necessarily a low priority issue. Perhaps we can get some guidance from the EarthByte team that wrote the initial implementation.