This commit updates geth to 1.8.17 and adds a possibility to enable metrics during compilation time.
The cascade of issues forced us to upgrade geth to 1.8.17 in order to allow enabling metrics during compilation time. 1.8.17 introduced `NodeID` refactoring and `enode` package which affected our peers pool and integration with Discovery V5.
The goal of this PR is to add an interface to verify MailServers. In this PR, MailServers are hardcoded in status-go. The next iteration will use a smart contract.