Update harvard7de.csl

Sorry, I am a very newcomer in editing styles. I want to create a new style called "gfpm-bas-harvard7de" by editing "harvard 7 de", because this style is quite similar to my needs. 

I made the following alterations:

- cite (Ex.): "Pfleiderer, 2014, S. 345" goes to "Pfleiderer 2014: 345"
- cite (Ex.): "Helms; Phleps, 2014, S. 345" goes to "Helms / Phleps 2014: 345"
- biblio (Ex.): new: Helms, Dietrich (2008). "What's the difference? Populäre Musik im System des Pop." In: PopMusicology. Perspektiven der Popmusikwissenschaft. (The latter titel is in italics!) Hg. von Christian Bielefeldt u. Udo Dahmen u. Rolf Großmann. Bielefeld: Transcript.
- biblio: I didn't manage to edit the following option: bibliographic entry of a proceeding or edited volume as a whole, e.g. with the editor-names in front of the entry.

I am looking forward to beeing supported in my edition in any way! Thanks a lot! 

Here you will find the standards of GfPM (Gesellschaft für Popularmusikforschung) Germany, which I tried to implement in the new style: http://www.aspm-samples.de/hinweise.html