Nicer serialization of database bibtex mode

[koppor]

If I switch to bibtex mode, JabRef writes

@Comment{jabref-meta: DATABASE_TYPE:BibTeX;}

Biblatex mode is

@Comment{jabref-meta: DATABASE_TYPE:BibLaTeX;}

Proposal: no use of uppercase letters

@Comment{jabref-meta: databaseType:bibtex;}
@Comment{jabref-meta: databaseType:biblatex;}

Reason: consistency with other metadata. See https://github.com/JabRef/jabref/blob/master/src/test/java/net/sf/jabref/importer/fileformat/BibtexParserTest.java#L1431

I know that we both have camelcase and usage of dashes and underscores. The JabCon addition by Jörg (saveOrderConfig) used the camelcase and we should not introduce other serialization kinds, should we?

[koppor]

You keep BibTeX and BibLaTeX (instead of bibtex and biblatex) because of koppor#73? 😇