Use a proxy for new release detection #1622

Give the possibility to set a proxy server for the new release detection and update process.

Especialy for server that don't have a direct access to internet.

If the server allows our Http class, you can already configure the proxy server URLs via #1471.

If the server doesn't allow our Http class, we can add a browser based check.

Reverting this ticket back to its original description, since a browser-based check is limited by the same origin policy, that approach isn't doable.

Marking as a dupe of #1471.