Update citation format to CSL-JSON

[gaurav]

The two main ways of representing citations in JSON appears to be CSL-JSON and BibJSON. CSL-JSON is a much more sophisticated and complicated format, but is supported by several NodeJS libraries (e.g. citeproc) that can convert it into citations in multiple formats. BibJSON is a much simpler format, but is only supported by citation-js, which I haven't been able to get working in Vue yet. Rod Page has a nice comparison of the two formats.

PhyloRegnum stores citations as structured data, which I would like to retain in the Phyx files we produce. Since we don't need to do much in terms of formatting for now, I'm currently writing the regnum2phyx script (#63) to store citations in BibJSON. Given that its supported more broadly, we might eventually want replace this with CSL-JSON, so I'm opening an issue to track this.