Add support for setting curators for each phyloref separately

[gaurav]

This has been proposed for phyx.js at phyloref/phyx.js#119

Once it is implemented there, we should add the user interface support for it to Klados.

[gaurav]

• Currently, we have parity between how phyloreferences and phylogenies work: you can set a default for the entire file, and then you can edit each individual node if you want (once Implement support for editing multiple taxonomic units at a single phylogeny node #228 has been implemented).
• I should test to see how this works with Open Tree of Life phylogeny across domains

[gaurav]

Is this a duplicate of #242?

[gaurav]

We can move this into Klados v1.0 but only if we can remove an equivalent amount of stuff from Klados v1.0.