Signs for thermoelastic surface deformations

The signs for surface deformations currently returned in all of the functions described here use the coordinate system and sign conventions used in Hello-Vinet, but these are perhaps backwards from what one might expect. The HR surface of the test mass is at negative z while the AR side is at positive z. While thermal lenses need to be added to a surface map, the surface deformations so defined also need to be subtracted.

These signs are furthermore the opposite of what's in finesse-fenics and usually the results of other FEA simulations more generally.