SV2 Proxy to support automatic pool fail over (and solo mine) on protocol-inconsistent messages

[rrybarczyk]

SV2 Proxy should support automatic fail over to a secondary and tertiary pool if it receives unexpected messages from the Upstream pool. If the secondary and tertiary pools also fail for any reason, the default behavior of the proxy should be to solo mine.

[TheBlueMatt]

As long as "unexpected messages" includes rejecting self-selected templates.