created ultravist and omnipaque from structure formula

[maxrohleder]

unable to reproduce how ultravist was created, so recreated it from structure formular too.

Created materials with weightedAtomicComposition() following the convention to be usable with the utils. (eg. computeMolarMass)

please review.

[akmaier]

Can you also submit the code that created the material? It would be great, if that code had references to the sources that were used.

Best,

Andreas