Replace gson library by jackson

Hawkular uses two json libraries: jackson for REST endpoint (as it is embedded in RESTEasy) and gson for BUS component.

If we want to re-use a REST data model into BUS context, we need to enable the model twice with jackson and gson annotations, or to use a workaround, as deal with plain json formats.

This JIRA is to track the replacement of gson library by jackson library in BUS context and its dependencies.