Add QFlag operators for MoleculeChange enum.

Change-Id: I40978672a0290adb2ddece0ab9f5cdf74d827f78
Make QtGui::Molecule's add* methods override Core::Molecule.

Otherwise the unique ids are not generated and removing
atoms/bonds is broken.

Change-Id: Id3590cb4bc56b0937f95f4f3cd80f600c8f9f158
Add obabel bond perception.

obabel doesn't explicitly support bond perception, but by
converting an xyz file to cml, bond perception is performed
by default.

Change-Id: Idb89903cf05e00b54c4dcfb3c20db9f14523413e
Merge topic 'obabel-bond-perception' into master

25464d66 Add obabel bond perception.
0a05bfda Make QtGui::Molecule's add* methods override Core::Molecule.
ac31041f Add QFlag operators for MoleculeChange enum.