Prevent funding explicit ethereum addresses on consensus

[matevz]

Fixes #23 .

Depends on #11.

Before:

$ oasis accounts transfer 0.1 0xDce075E1C39b1ae0b75D554558b6451A226ffe12 --no-paratime
You are about to sign the following transaction:
Method: staking.Transfer
Body:
  To:     oasis1qqxlf9za3py8d6462wkwm49r4t294slncy97zhlr
  Amount: 0.1 TEST
Nonce:  7
Fee:
  Amount: 0.0 TEST
  Gas limit: 1264
  (gas price: 0.0 TEST per gas unit)

Network:  testnet
ParaTime: none (consensus layer)
Account:  test

$ oasis accounts withdraw 0.1 0xDce075E1C39b1ae0b75D554558b6451A226ffe12
You are about to sign the following transaction:
Format: plain
Method: consensus.Withdraw
Body:
  To: oasis1qqxlf9za3py8d6462wkwm49r4t294slncy97zhlr
  Amount: 0.1 TEST
Authorized signer(s):
  1. MJ2XCjkj132C9YWpDUSQFjkCTI8bSw8bi0w9EwwE1Bg= (ed25519)
     Nonce: 0
Fee:
  Amount: 0.0011311 TEST
  Gas limit: 11311
  (gas price: 0.0000001 TEST per gas unit)

Network:  testnet
ParaTime: sapphire
Account:  test

After:

$ oasis accounts transfer 0.1 0xDce075E1C39b1ae0b75D554558b6451A226ffe12 --no-paratime
Error: signer for address '0xdCe075E1C39b1AE0b75d554558B6451a226FFE12' will not be able to sign transactions on consensus layer
Use --force to ignore this check
$ oasis accounts withdraw 0.1 0xDce075E1C39b1ae0b75D554558b6451A226ffe12
Error: signer for address '0xdCe075E1C39b1AE0b75d554558B6451a226FFE12' will not be able to sign transactions on consensus layer
Use --force to ignore this check