Add ability to output to GAMBIT neutral file format
Allow user to specify a
.neu file as output from the CLI and the GUI. The GAMBIT neutral file format specification can be found at http://web.stanford.edu/class/me469b/handouts/gambit_write.pdf.
It might also be useful to eventually implement a
readNEU method or to include more shape types supported by the GAMBIT format, but for now it's easiest to cover a base case of triangles and tetrahedra in 3D space.