WebServices: Created ExtendedProblemsView and method sleep() in RedDeerHelper

RedDeerHelper provides method sleep(seconds), which can be used to estimate
necessary time to wait until ws validation is done (can't be used JobIsRunning
because the validation is not represented as a visible job)

ExtendedProblemsView is designed to test problems/warnings displayed as a result
of ws validation (there is a wait to ensure that validation shows problems
before problems are obtained from Problems view)
WebServices: more RedDeer in tests, using ExtendedProblemsView to get problems

Created JAXRSValidatorPreferencePage in order to reimplment JaxRsValidatorTest
with RedDeer.

Using more RedDeer in RESTfulHelper.

Refactored error/warning assertion in RESTfulTestBase.

To some tests was necessary to add sleep() method to ensure that ws validation
reflected expected results to the JAX-RS Explorer