show graphite/anthracite/ES req errors. fixes #52

any error basically, from the client side renderer
now gets displayed both where the graph should be,
as well as in the console.

verified with:
* bad graphite url (unknown dns)
* bad graphite url (bad port) / stopped server
* bad anthracite url (bad port)
* bad request url that errors graphite:
  data: data.join('&') + "&target=avgSeries('foo',12,6464, bar)",
* disabled CORS for graphite
* anthracite CORS

they don't go into the details of why, but it's good enough i would say