To make debugging of the heartbeats a bit easier, this commit adds a stringify package which can show even very complex objects in a nice readable format like:

Heartbeat {
    nodeId: "c0a2918db00514d655f2b82199c6aedda234f807"
    mainStatement: OpinionStatement {
        previousStatementHash: <nil>
        nodeId: "c0a2918db00514d655f2b82199c6aedda234f807"
        time: 1567213114
        toggledTransactions: [
            ToggledTransaction {
                transactionId: 0x29f54622b0df47c864ceca1a5bb4ed84fb7dbbc1b4a6d9a029f79572b86f4d3c68bcca30b08953ac9d217a667facac7d4aa0
                initialStatement: true
                finalStatement: false
            },
            ToggledTransaction {
                transactionId: 0x774f74040c249b73ec4c390352e3191438899c166863b86765e1ef8546ea735bd0ff28dea6e35c9b7d66b35a5703b0c7fe63
                initialStatement: true
                finalStatement: false
            },
        ]
        signature: 0x57fa4ba799a2312b4e8561b144d9386703fce7f128c30c9ec2eeec73693878704d0a176cd4563f5afa8f5ceabdd2552f42bd17cd82363fc0bd1c1386edf914d401
    }
    neighborStatements: map{}
    signature: <nil>
}

To be able to make the vote packages smaller, we have introduced a hash compression mechanism. While hashes can usually not be "compressed" due to limits in information theory, nodes in the IOTA network already know about relevant hashes upfront. We therefore only need to be able to exchange which hash we mean, when we exchange votes. This commit introduces a novel data structure, that uses radix trie like mechanisms, to create a very compact representation of a tx hash that can be understood by others. It allows us to compress the hashes from 49 bytes to 2-3 bytes which is a 94% compression rate.

Improve README about docker command

Resolve "go vet" errors

Fix: wrong error check after opening db

Improved []byte<->string conversion

Manually enable/disable plugins