JBIDE-12175 Automatic namespace completion in Facelets files

Implemented name space storage for user defined namespaces.
Automatic namespace completion is added for the namespaces that are not
defined within the page:
- xmlns:*-attribute names
- xmlns:*-attribute values
- tags having a prefix that is not defined within the page
All the default prefixes of the Tag Libraries and the custom user defined prefixes are
taken into account.