jbpm-workitems: use cxf-api instead of cxf-bundle-jaxrs

 * the cxf-bundle-jaxrs is bundling basically everything
   cxf related and also bring a lot of other transtitivite
   deps, which is not what we want. To satisfy the
   illegal-transtitive-dependency-check it is enough to
   depend just on cxf-api.

 * removed the resteasy-jaxrs-api dep. as it collides with
   the CXF stuff (e.g. NotSuchMethodError) and it seems
   it not needed anyway (tests pass and the
   transitive-dependency-check too)
jbpm-human-task-core: JAXB/JSON serialization correctness (because of kie-remote-jaxb-gen issues)
JBPM-4483 - error on broadcasting signals - test cases
adjustemnts to timer based test to not cause false alarms
jbpm-human-task-core: JAXB/JSON serialization correctness (because of kie-remote-jaxb-gen issues)