parse biological assemblies described in PDB files

the REMARK 350 section which described biological assemblies is parsed.
We don't do anything with the information yet.
add assembly information to Mol
simplify option handling logic a bit

All the render functions now to through the same handleStandardOptions.
This cuts down on redundancy when processing the options and will make
it simpler to introduce new option for all of the render methods. Point
in case: Handling of symmetry-related copies.