vertex/facewise colour from file

[drmowinckels]

Currently, ggseg3d works in an unefficient way. Where each segment of the brain is its own list of faces and vertices, added to the plot in a loop, and each segments get an individual colour.

This is inefficient because:

• loops are slow.
• requires to keep stored the entire vertex and face list for all atlases.
• is less flexible in terms of what type of data you can project onto the mesh surface.

Ideally, the package would store a single mesh-data object of the entire brain (like the glass brains currently are), and functions that could project colours directly to the face of the mesh.
Particularly, this should at first be developed to work by translating Freesurfer annotation files to .ply files that include colour.