"Instance" library registrations as xml file

[maraf]

Instead of registering libraries in the templates, we could create a format that editors could use to find information for intellisense.
We already have a autoregister.xml and could use it even more to define "instance" registrations.

• Edit in CMS
• Convenient place in module structure, but added manually by module
  • Requires Modules can't register libraries in the template #471
• Support multiple XML sources in TemplateParser. It shouldn't be part of parser. It should simulate "lazy" registration from postinit.