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-296 - Added support for case insensitive sorting.

Modified QueryUtils.toJpaOrder(…) to apply lower criteria if ignore case on Order is set to true and the property being sorted is of type String. Upgraded to Spring Data Commons 1.6.0.BUILD-SNAPSHOT along the way.