ISPN 4728 ISPN-4775 ISPN-4773 Various UberJar + Distribution fixes

A bunch of stuff:

https://issues.jboss.org/browse/ISPN-4728
https://issues.jboss.org/browse/ISPN-4769
https://issues.jboss.org/browse/ISPN-4770
https://issues.jboss.org/browse/ISPN-4771
https://issues.jboss.org/browse/ISPN-4773
https://issues.jboss.org/browse/ISPN-4774

ISPN-4773
    - Move distribution to its own module
    - Use ant instead of assembly descriptors to prepare the distribution for simplicity/maintenance
    - Group JavaDoc APIs
    - Provide a documentation index which points to javadocs, schema docs and jmx docs
    
ISPN-4728 Use UberJars as main distribution packaging

ISPN-4774 Demos
    - Rearrange demo paths and depend on uber-jars
    - Drop directory demo

ISPN-4769 XSD Documentation builder fixes
    - show documentation annotations for restrictions
    - handle xs:list simpletypes
    - use the local namespace in the JDBC XSD where it is missing
    
 ISPN-4770 PublicAPI doclet should not crash on empty component types (i.e. generics without type parameters)
    
 ISPN-4771 Introduce a DocleMultiplexer to combine doclet execution in one
    - Clean up doclets to better adhere to the JavaDoc spec