allowing the 'ws-server' to process plain http GET requests

This is a port of the changes proposed in https://github.com/aphyr/riemann/pull/422

I've switched the uri's to /index and the 'q' parameter is now 'query' to be consistent with the existing websockets uris.

provides:
    GET /index list of all events in the index
                query parameters:
                'offset' - offset of first item to return
                'limit'  - max number to return (defualt is 250)
                'query'  - riemann query to match events against
index-handler kinda does the split, have been staring at how to combine ws-index-handler and http-index-handler, while they obviously doing the same thing, just in not completely completely compatible ways. 

on the up side now that the host/service uri's have gone it should be a lot easier to merge the two.