added export of 3D meshes to TetGen smesh
added support for creating TetGen smesh files for meshes with static layer thickness
added tetgen export option for 3D meshes to gui
renamed and documented new methods
removed method for parsing poly-files
only 3d elements are analysed, const qualifiers added
Merge pull request #408 from rinkk/3DMeshesToTetGen

3d meshes to TetGen