RESTEASY-900: Return text representation of validation violations.
Merge https://github.com/resteasy/Resteasy

Conflicts:
	jaxrs/providers/resteasy-validator-provider-11/src/main/java/org/jboss/resteasy/plugins/validation/ValidatorContextResolver.java
Merge pull request #354 from ronsigal/master

Validation: RESTEASY-899, -900, -907.