Citation getter function

[haneug]

Is your feature request related to a problem? Please describe.
OPI would not be possible without the great work done by the ORCA developers. To give them their deserved credit, we should add a function to make the citations (which are already in the gbw file) easily accessible also with OPI

Describe the solution you'd like
A getter function for the citations.

[timmyte]

@haneug
Doesn't ORCA also write bib file at the same time?
If yes, I would focus on that, as this can easily be fed into reference management software like Zotero, Jabref,...