Bump CXF version to latest 3.1.6

Investigate if 3.0.9 or 3.1.6 is the best fit for us and update the dependency version

org.apache.cxf:cxf-core ............................... 3.0.3 -> 3.1.6
org.apache.cxf:cxf-rt-frontend-jaxrs .................. 3.0.3 -> 3.1.6
org.apache.cxf:cxf-rt-rs-client ....................... 3.0.3 -> 3.1.6
org.apache.cxf:cxf-rt-rs-extension-providers .......... 3.0.3 -> 3.1.6
org.apache.cxf:cxf-rt-rs-security-cors ................ 3.0.3 -> 3.1.6
org.apache.cxf:cxf-rt-transports-http-jetty ........... 3.0.3 -> 3.1.6
org.apache.cxf:cxf-testutils .......................... 3.0.3 -> 3.1.6
upgrade-to: 3.0.9
rel-date: Mar 23, 2016
rel-notes: https://cxf.apache.org/cxf-309-release-notes.html
modules: hippo-site-toolkit
advice: upgrade to 3.0.9