Combine crystalforms and assemblies into assemblies.yaml

[phraenquex]

As remembered in #1225: assemblies and crystalforms must be declared in a single file, because the latter references things in the former, and it needs to be real-time validatable for users.

(Notepad++ does this automatically, I discovered on the weekend, with content-completion.)

@CFWild suggested the change is simple programmatically .

[ConorFWild]

Fixed on xchem-align with 51ee726 and ligand_neighbourhood_alignment with 0702c80

Safe to close once tested on other systems @tdudgeon @phraenquex

[phraenquex]

Final action: change xtalforms.yaml to crystalforms.yaml

[Waztom]

@kaliif to check and test output for uploading to Fragalysis.