Updated service definition with uip (ip overrid) and ua (user agent over...

Hi, 
This is a pull request to reflect recent undocumented changes in google analytics measurement protocol.
(See this post on google groups : https://groups.google.com/d/msg/google-analytics-measurement-protocol/8TAp7_I1uTk/CIJtk3W3L-UJ  )

In case you want to forward google analytics request using a server, Google will always see your server ip and server http client user agent. To address these problems you can now use :
* The *uip* parameters can be used to override ip address
* The *ua* parameters can be used to override user agent

Hope you'll be interested in this pr !