DATAJPA-314 - Improve namespace XSDs to avoid IDE warnings.

Removed the explicit pointer to the XSD location of the context namespace as this apparently seems to cause duplicate imports of the tool namespace XSD.
DATAJPA-300 - Specifications are now more lenient against null values.

Static factory methods on Specifications are now more lenient regarding null values eventually evaluating to null predicates on concatenation attempts.
DATAJPA-292 - Manually defined queries can contain like expressions now.

This commit introduces support for JPQL inline like expressions such as "… like ?1%". The implementation will detect those expressions and turn the query back into a valid JPQL one. On query execution the parameters will be bound according to the like expression defined in the query.