Add MopacTS class

This was removed as Mopac's semi-empirical methods
are not sufficient to find useful TS geometries. It
may prove handy for NEB calculations to provide fast
geometries, but it will need some cleaning up.
Correct multiplicity writing in input files

Multiplicity was calculated and placed on in qm.geometry.
As multiplicity is now a molecule parameter, it is now
read from the molecule.
Remove NotImplementedError from inputFileKeywords

The inputFileKeywords has been generalized in gaussian.py
and has already been written in.
Fixup double-ended search algorithm

The QST2, Saddle, and NEB calculations have been placed
into one method. Previously the NEB was separate, but the
methods are quite similar.

The partial optimization of the reactant and product
geometries is now under the relevant calculator. This is
done for all double-ended methods and is a more elegant way
if handling the calculation.