Add VisualArtwork to Comic contributor properties
Add VisualArtwork to Comic contributor properties

artist, colorist, inker, letterer, and penciler are desired to describe Comics
in a way that supports the Grand Comics Database (comics.org) description of
comics in a straightforward manner (that is, without requiring Role
reification). These properties are also useful for VisualArtwork.

Fixes #455.

Signed-off-by: Dan Scott <2591e5f46f28d303f9dc027d475a5c60d8dea17a@coffeecode.net>

gkellogg/schemaorg,vholland/schemaorg,URXtech/schemaorg,vholland/schemaorg,gkellogg/schemaorg,cesarmarinhorj/schemaorg,vholland/schemaorg,dbs/schemaorg,lanthaler/schemaorg,quantegy/schemaorg,vholland/schemaorg,unor/schemaorg,haonature888/schemaorg,tfrancart/schemaorg,mortizbank/schemaorg,dbs/schemaorg,ynh/schemaorg,quantegy/schemaorg,twamarc/schemaorg,haonaturel/schemaorg,vemmaverve/schemaorg,schemaorg/schemaorg,tfrancart/schemaorg,schemaorg/schemaorg,schemaorg/schemaorg,haocafes/schemaorg,tfrancart/schemaorg,hschema/schemaorg,ynh/schemaorg,unor/schemaorg,tfrancart/schemaorg,twcctz500000/schemaorg,haonature888/schemaorg,schemaorg/schemaorg,ya7lelkom/schemaorg,haocafes/schemaorg,dbs/schemaorg,pwz3n0/schemaorg,haonature/schemaorg,vemmaverve/schemaorg,mortizbank/schemaorg,lanthaler/schemaorg,ya7lelkom/schemaorg,hschema/schemaorg,cesarmarinhorj/schemaorg,pwz3n0/schemaorg,lanthaler/schemaorg,dbs/schemaorg,sdo-sport/schemaorg,haonature/schemaorg,pwz3n0/schemaorg,ynh/schemaorg,sdo-sport/schemaorg,twcctz500000/schemaorg,mortizbank/schemaorg,hschema/schemaorg,unor/schemaorg,twamarc/schemaorg,gkellogg/schemaorg,twamarc/schemaorg,sdo-sport/schemaorg,URXtech/schemaorg,schemaorg/schemaorg,haonaturel/schemaorg,quantegy/schemaorg,ya7lelkom/schemaorg,cesarmarinhorj/schemaorg,gkellogg/schemaorg