Add channel parameter

Problem/Motivation

Add ability to add an optional channel parameter.

A channel parameter is an optional parameter that allows you to track usage under your client ID by assigning a distinct channel to each of your applications. To use the channel parameter, include it in the request URL together with the client parameter used for passing the client ID.

Proposed resolution

We could add one channel parameter per application by adding it to geolocation map parameters settings form.

User interface changes

Add an additional textbox to capture the channel parameter under "Optional Google parameters" in geolocation google map parameters settings form.