TRC blockexplorer update, new network params.

 - cryptocoinexplorer.com recently closed, now using bitinfocharts.com
 - non-fatal warning for users running client < 0.8.0.4
 - seed3 re-added to hardcoded seedlist
 - net network parameters, hopefully suitable for a larger audience
 - using newly introduced p2pool modular networks

 - IDENTIFIER & PREFIX updated because of the new values