Refactor scopes for Servlet API jar

When I added a reference to ServletContext in resteasy-core, a test in resteasy-rxjava failed because it couldn't find ServletContext. That's because the test doesn't run in Wildfly, so jboss-servlet-api_3.1_spec doesn't get provided. We're saying that resteasy-rxjava needs to have an explicit dependency on jboss-servlet-api_3.1_spec, even though it doesn't directly reference anything in jboss-servlet-api_3.1_spec.

For RESTEasy applications running in Wildfly, jboss-servlet-api_3.1_spec is "provided" by the servlet container. For a standalone program using, say, resteasy-netty4, NettyJaxrsServer is serving as an embedded servlet container, and, by analogy, it should supply jboss-servlet-api_3.1_spec. That is, it should have a dependency on jboss-servlet-api_3.1_spec with scope "compile".

The same change would appropriate for resteasy-netty and resteasy-undertow.