Refactored UsageValidator

Now read all usages, check if exists, valid duplicates.
Validator can resolve both traits and classes. Namespaced, or in root
namespace.
PDTT Integration

Validation in core not work still need improvement but ErrorReporting
work like on PDT core tests
Other changes:
* pom xsd
* clean up
* some import
* feature.xml fix
* validation optimise (only one run)
Git ignore
Tests works without UIThread

Now life will be easier
Merge branch 'master' of github.com:pdt-eg/Core-Plugin