* Added abstract class TexturedMesh to provides support for different mesh implementations taking into account four different kind of textures: None, Image (by vertices or by texture indices),  Colored vertices, Colored faces. For the last two ones, number of colors and density map have to be provided.
* Added helper to deal with color palettes, and density plots
* Added Primitives: SpringMesh, CurvedSpringMesh and SegmentedTorusMesh. With IcosahedronMesh, the four of them extend TexturedMesh, and support the four kind of textures.
* Added tests for these four classes, to test four different textures and also with animation to change the texture