Multiple nodes with the same key causes problems

[SurfingNerd]

Although it is advised to run a fail over setup, the backup node should never use the same keys than the active node.
We need to make sure that the malicious detection detects this behavior so that nodes using this wrong setup get identified and reported as malicious early on.

Store that information in the HBBFT Memorium.

[SurfingNerd]

should in the next step handled as malice report: #75