Configurable box padding for orbital cubes

[md-5]

This patch adds a new "boxPadding" option to molecular orbital visualisation.
It allows changing the amount of padding added to the orbital render cube (defaults to old value of 2.5).
By increasing it to a larger value you can see full orbitals that are otherwise cut off.

Very useful for observing large / diffuse Rydberg states

[ghutchis]

Thanks!

While I'm happy to look at this for the final 1.3 release, I'd really like the option added to Avo2:
http://github.com/openchemistry/avogadrolibs/pulls/

[md-5]

Hi Geoff,

Using Avogadro to look at output files generated by ORCA. Haven't yet tried Avogadro 2, but skimming the source I don't see anything related to ORCA, although it could be abstracted into an input library.