Restrict blacklisted nodes to a maximum amount of rounds (#631)

* Restrict blacklisted nodes to a maximum amount of rounds

This commit adds a maximum amount of rounds that a node can be blacklisted.
After the number of rounds passes, the node is automatically redeemed.

The blacklist stores the maximum number of rounds as a maximum orbit (uint16).
If a node has been blacklisted more than this maximum orbit ago, it is redeemed.

The maximum orbit / number of rounds can be changed via consensus by a local config change.
When a node proposes a new block, it is able to increase or decrease the maximum orbit by 1 according to the distance from its local config.

Nodes reject blocks that their maximum orbit changes for more than 1.

Signed-off-by: Yacov Manevich <yacov.manevich@avalabs.org>

* remove md.Seq++

Signed-off-by: Yacov Manevich <yacov.manevich@avalabs.org>

* Get rid of nodeConfig in node

Signed-off-by: Yacov Manevich <yacov.manevich@avalabs.org>

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Signed-off-by: Yacov Manevich <yacov.manevich@avalabs.org>

Author: yacovm