server logs exception messages on internal server error. Closes #4
added first cut at discovery service with associated client script
service addresses returned from discovery service use request.get_host() instead of hardcoded hostnames
added discovery notes to index.html
added background image to index.html
modified opacity of background image for index.html
reorganizing taxii_services app
removed full opacity yeti image
removed unnecessary css rule
Merge branch 'discovery'