Explicit POM dependencies in nuxeo-connect-client

nuxeo-connect-client has a dependency on commons-codec which is implicit and resolves to version 1.2. We should use explicitly the same version as the one in Nuxeo: 1.9.

(This is a problem only when running unit test org.nuxeo.connect.update.standalone.commands.AbstractCommandTest.testInstallThenUninstall from Eclipse, which picks 1.2 and fails to resolve org.apache.commons.codec.binary.Base64.decodeBase64(String))