Proposal for additional safety checks for recipient address

[zharjac]

In order to minimize the possibility of sending funds to a wrong address, I propose to implement some simple additional checks of the destination address:

1. Log a history of sent-to account addresses and warn the user when sending to an address that was never used before.
2. Check the balance of the destination address and if 0 warn the user (reasoning: it might be either a never before used address or simply a wrong address).
3. Implement Feature: Warn on attempt to send Ether/Tokens to known-insecure accounts on Mainnet #2608