Fix for Request headers having non-standard keys not readable by RG dash

Headers from Rack env have keys which have an HTTP_ prefix, are uppercase, and an underscore separator. Raygun dashboard expects them to be of form { "request": { "headers" : { "User-Agent" }}}. Currently the headers and IP address show Not Provided in the request tab. This updates the headers(rack_env) function to format them as expected.

This uses the titleize method, from ActiveSupport - is this available/imported in all Rails environments?

Also corrects the IP address to the expected key