Allow custom data to be passed for server on download requests

In order to collect download statistic for online downloads the IFW should allow custom data to be passed to server on every HTTP request.

For maximum flexibility, the IFW should allow any name/value pairs to be passed as an URL query string in every HTTP request.

The actual name/value pair to be passed on server is likely to differ based on installers and need, but for example:

• Qt opensource installer could pass some unique machine ID to server side -> Allowing anonymous statistic collection
• Qt commercial installer could pass some customer specific ID (derived from license key) to server side -> Allowing mapping statistics to customer