Loss of template provider is not gracefully handled

[wizkid057]

The template provider is checked on startup, but the loss of the template provider at a later time can currently result in mining of stale work. It can not do non-pooled mining failover without a valid template, and it won't disconnect stratum clients for failover because this only happens with the loss of connection to the DATUM server, not currently for the loss of the template provider.

Need detection of this loss and appropriate recovery by either disconnecting stratum clients so they can fail to an alternate, or by potentially having an alternate/backup/secondary template provider that the gateway can utilize.