Re-enable descriptions for CodeNarc

from line 120 of CodenarcParser.java:

//TODO: the following depends upon a patch to CodeNarc 0.9 - so should be exception tolerant
// get the contents of the embedded Description element
//expectNextTag("Description");
//ret.setPopupMessage(getNextText("Missing Description"));

CodeNarc is now at version 0.15 and writes out the description in it's xml report, but currently this section of the violations plugin is commented out. (I would have fixed this myself, but I had trouble getting the plugin to compile without doing some goofy stuff) It would be really helpful to have the description as well as the rule name for CodeNarc.