Stereo Chemical tags are not recalculated

[EBjerrum]

When editing the molecule, the stereochemical tags around e.g. cis-trans bonds are not recalculated. This can result in them being incorrect. The sanitization code also does not trigger a recalculation.

[jacktday]

Setting prepareMolsBeforeDrawing seems to fix this bug as well

[EBjerrum]

Should be fixed with the user settable drawing settings intriduced in #36