Added net templates for various 3D shapes

Summary:
Added templates for rectangular prism nets, square pyramid nets, triangular
prism nets, tetrahedron nets, and octahedron nets to graphie-to-png.

Test Plan: Visit graphie-to-png.khanacademy.org. Load examples 22..26

Reviewers: alex

Reviewed By: alex

CC: elizabeth

Differential Revision: http://phabricator.khanacademy.org/D4419