Add auth provider: NoAuthenticationProvider
Move NoAuthenticationProvider under extensions/

New auth providers shouldn't go in guacamole-ext, which is strictly the
API used by extensions to Guacamole. Instead this should be a separate
project like "guacamole-auth-noauth", and should go under extensions/.
Fix auth extension naming and groupId.
Fix author and name.
Extract NoAuthConfigContentHandler. Partial cleanup.
Clean up auth provider code, avoid NPE with property. Use getRequiredProperty() for required property.
Clean up parser. Add sanity checks against XML. Add documentation.
Remove unexpected element sanity check for now.
Replace README.rst with standard README.
Add backup files to .gitignore
Fix whitespace errors.
Use latest guacamole-ext.