Removed OpenBabel dependence from writing gaussian input files.

We do the text manipulation (reading a .mol file, writing a .gjf) 
on our own now, instead of using OpenBabel.
May be slightly more fussy about the input .mol file formatting, but as these
are made automatically by RDKit it's unlikely they will change.
Removed OpenBabel dependence from writing mopac input files.

We do the text manipulation (reading a .mol file, writing a .mop) 
on our own now, instead of using OpenBabel.
May be slightly more fussy about the input .mol file formatting, but as these
are made automatically by RDKit it's unlikely they will change.
Remove CML from example input file.

Without OpenBabel we cannot read CML.
If we re-enable it, revert this commit.
Tweak the molecule drawing - make bonds a little shorter.

I think this looks a little better, at least on the molecules I tested it on.
Get the qm.molecule.rd_build to use the molecule.toRDKitMol method.

This reduces a lot of code repetition, although there were a couple of
minor differences between the methods. Namely:
 1) in the QM module we need to return a dictionary of mappings
 2) in the QM module we need to keep hydrogen atoms
Remove unnecessary imports.
Remove unnecessary SMILEwriter code.