Create annotation for citations

[felixreimann]

A @citation annotation shall hold information for citations for a specific class.

When an optimization is started, all used classes with @citation could be gathered and, as an information, printed out to the logger.

The GUI could show them.

[michaelhglass]

Possible list of features:

• Multiple citations per class/element required (careful since multiple annotations of the same type requires Java 8 - otherwise a @Citations might be required with nested @citation)
• The respective representation of the annotation should follow one internationally accepted style like Harvard etc. I would suggest relying on the programmer to adhere to a certain simple style and not integrate a full-fledged BibTeX/Biber parser
• Citation should also find its way into the documentation without duplicating entries in the comment

[felixreimann]

Regarding your first point: I think it is time to upgrade to Java 9. Thus, another @Citations is not necessary.