Add abstract and keywords to .csv and to .bib file

[koppor]

Currently, the .csv and .bib do not contain the abstract and keywords. An abstract and keywords is good to be communicated to search engines or meta data.

This is a pre-condition for #23.

[koppor]

Maybe the tool for that can also fix #12.

Instead of letting the proceedings.tex generate the .bib and .csv file, it could also be done using an external script.

[koppor]

#17 discusses the extraction and storage of the meta data

[koppor]

This is also used for the submission of Dublin Core data elements for the GI. (Documentation: https://github.com/gi-ev/LNI-proceedings#submitting-to-the-digitale-bibliothek-der-gi)

Currently, metaExtract.py is the basis for that process.