Add method to retrieve given annotation linked to object.

Method useful to retrieve annotation like modulo annotation
added at import time.
Fix class cast exception.
Fix query to load annotations.
Add tests for modulo retrieval.
Add modulo namespace to constant.
Add test to create XML annotation.
Add modulo ns to pojos and add test using modulo ns.
Fix documentation.
Add pixels to the list of supported type. Test added too
Improve Java doc.
Merge pull request #587 from jburel/rebased/develop/modulo-retrieve

Modulo retrieve (rebased onto develop) Merging before we start refactoring tests.