[JSON-RPC] Add xbmc.gameclient as a valid add-on type.
[JSON-RPC] New parameter for Addons.GetAddons, "uninstalled", to get add-on info from remote repos.

Example:

Addon.GetAddons( { "method": "Addons.GetAddons", "params": { "type": "xbmc.addon.video", "enabled": "uninstalled" } } )