add support for evan.network chains

[S3bb1]

This pull request adds support for evan.network public authority chains. It contains 2 networks, the testnet known as evan.network testcore and the mainnet known as evan.network core chain.

Website: https://evan.network

Github: https://github.com/evannetwork
Wiki: https://evannetwork.github.io/
Faucet for testnet: https://gitter.im/evannetwork/faucet

Blockexplorer Testnet: https://testexplorer.evan.network
Blockexplorer Mainnet: https://explorer.evan.network

Thank you!

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[S3bb1]

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[parity-cla-bot]

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Parity Technologies CLA Bot