Show texture map using parameterization

[MarkGillespie]

This adds a new parameterization visualization style which uses polyscope's existing texture mapping utilities to texture surface meshes using to the given parameterization.

(There's also a small modification to gl_engine.cpp to provide line numbers for shaders which fail to compile, which makes it easier to debug them)

[nmwsharp]

Thanks for submitting this, and sorry for the super long delay. I overhauled an integrated this in #239, now merged!

The main tweaks vs. here were (a) make the texture quantities share most cost with scalar/color quantities and just take a parameterization as a reference, because you might want many color-maps associated with a single set of UVs, and (b) use the new ManagedBuffer texture features, which were recently merged.

Let me know if that other merged PR missed anything or gives you any trouble!