Make 'registerServiceProviders' static

Suggested by @joshmoore and @rleigh-dundee.
merge develop -D org -I include -E exclude: PR 528 (Tile performance improvements for VMS and NDPI)
merge develop -D org -I include -E exclude: PR 574 (xsd-fu: Generalise language type mapping)
merge develop -D org -I include -E exclude: PR 578 (xsd-fu: Generalise language type mapping (2))
merge develop -D org -I include -E exclude: PR 583 (Reduce the number of JAI ImageIO registrations)
merge develop -D org -I include -E exclude: PR 585 (Update auto-generated documentation)