Oxygen 0.7.0

With some improvements and fixes that have accumulated during the last year, it is time for another release.
Changelog:
New localizations: Greek, German, and Chinese
Direction of attached hydrogen atoms can be set explicitly by user
Atom shape can also be a circle instead of a rectangle
Bitmap export with adjustable resolution
Support OpenBabel 3
Fixes for sum formula and molecule tooltip
Fix clipping of bonds
Fixed OpenBabel support