[with patch, positive review] polyhedral improvements: Schlegel diagrams, standard polytopes, multiplication, polars

apply versus 3.1.2; conflicts with #4164 patches

Apply to a vanilla 3.1.2 or 3.1.3; supercedes previous patch

This adds several enhancements such as Schegel diagrams, scalar dilation of polytopes, translation by a vector, built-in regular polytopes such as the 24-cell and cross-polytopes, and generation of polar duals. To make it easier to review this patch includes changes from #4164, so you just need one patch.

improved and re-based against 3.1.4

The trac_4256_v3.patch also incorporates the changes in #4164. Polyhedra can now be multiplied, scaled, translated, and the polar (dual) constructed. Several standard polytope families have been added.

The ambient_dim function overwrites the content self._dim thus making dim() return a wrong answer:

sage: p = Polyhedron(vertices = [[0,0,1]])
sage: p.dim()
0
sage: p.ambiant_dim()
3
sage: p.dim()
3

In the vertex_adjacency_matrix() docstring, maybe you should use 'binary' rather than '0/1'

In render_solid(), since you now have ambient_dim(), why not use it? It could replace the ugly test I put there.

Also for the 'special' polyhedron creation methods, it could be good to reuse the approach taken for graphs, where you have the Graph class and an instance of a special class called graphs where you have building methods for most interesting types of graphs.

The first item is a must-fix, the other three would be nice, but are not stricly essential.

supercedes previous patches, addresses review

The only thing left to do is to mark the lrs_volume() tests as optional. I forgot that in my initial review.

Anyway, apart from that, positive review

supercedes previous patches, addresses final review (optional tests)

OK, I made the lrs_volume tests optional. Thanks very much for reviewing this.

Merged 4256_v5.patch in Sage 3.2.alpha1