Add software and dataset to biblatex entry types

[Siedlerchr]

The most recent version of biblatex now has the new fields @software and @dataset
https://github.com/plk/biblatex/blob/dev/doc/latex/biblatex/CHANGES.md

The @unpublished entry type now also supports type, eventtitle, eventdate and venue.

We should add them as well.

[Siedlerchr]

Thank you for reporting this issue. We think, that is already fixed in our development version and consequently the change will be included in the next release.

We would like to ask you to use a development build from https://builds.jabref.org/master and report back if it works for you. Please remember to make a backup of your library before trying-out this version.