Allow patching of derived manifest details

[tomcrane]

I think Presley will allow us to just PUT the whole manifest again, but that's a bit heavyweight if I just want to update the title. I should be able to send a JSON patch with just the updated "label", "description" or whatever.

[mattmcgrattan]

Is patching MVP?

[tomcrane]

no, just putting it here for later.

[tomcrane]

OK, for now, sorting-room needs to allow user to edit the manifest label and description, but it will just re-PUT the whole manifest.