Disconnect nodes older than protocol version 70002 (Litecoin 0.8.3.7)

Why disconnect older versions?  A minority of users are failing to upgrade despite months of warnings.  Older versions are not safe.  The network as a whole will be healthier if everyone upgraded.

**Deployment Plan**
* https://litecoin.info/Alerts  Make alerts for protocol versions 70001 and earlier permanent.
* Warn loudly on social media that older versions will soon no longer be able to connect to the network.