accounts: Check if 'to' address is reserved

[matevz]

Fixes #7.

This PR checks, if the to address for Transfers, Withdrawals and Deposits is a known unspendable address:

• rewards pool address
• common pool address
• fee accumulator address
• governance deposit address
• native ParaTime address

User can override the check by passing --force switch.

Example:

$ oasis accounts transfer 10 pool:rewards
Error: address 'oasis1qp7x0q9qahahhjas0xde8w0v04ctp4pqzu5mhjav' is rewards pool address
Use --force to ignore this check
$ oasis accounts deposit 10 paratime:emerald
Error: did you mean --paratime emerald? Address 'oasis1qr629x0tg9gm5fyhedgs9lw5eh3d8ycdnsxf0run' is native address of paratime:emerald on testnet and should not be transferred to directly
Use --force to ignore this check
$ oasis accounts deposit 10 oasis1qr629x0tg9gm5fyhedgs9lw5eh3d8ycdnsxf0run
Error: did you mean --paratime emerald? Address 'oasis1qr629x0tg9gm5fyhedgs9lw5eh3d8ycdnsxf0run' is native address of paratime:emerald on testnet and should not be transferred to directly
Use --force to ignore this check
$ oasis accounts deposit 10 paratime:emerald -f
Warning: did you mean --paratime emerald? Address 'oasis1qr629x0tg9gm5fyhedgs9lw5eh3d8ycdnsxf0run' is native address of paratime:emerald on testnet and should not be transferred to directly
Proceeding by force as requested
You are about to sign the following transaction:
{
  "v": 1,
  "call": {
    "method": "consensus.Deposit",
    "body": "omJ0b1UA9KKZ60FRuiSXy1EC/dTN4tOTDZxmYW1vdW50gkUCVAvkAEA="
  },
  "ai": {
    "si": [
      {
        "address_spec": {
          "signature": {
            "ed25519": "MJ2XCjkj132C9YWpDUSQFjkCTI8bSw8bi0w9EwwE1Bg="
          }
        },
        "nonce": 3
      }
    ],
    "fee": {
      "amount": {
        "Amount": "2001535",
        "Denomination": ""
      },
      "gas": 400307,
      "consensus_messages": 1
    }
  }
}

Account:  test:alice
Network:  testnet
Paratime: cipher
? Sign this transaction? (y/N)

[kostko]

Instead of just denying, there should be a flag (like --force) that would still allow you to do it. For the reward pool address this is even required as otherwise it would be hard to actually fund the pool.

[matevz]

Instead of just denying, there should be a flag (like --force) that would still allow you to do it. For the reward pool address this is even required as otherwise it would be hard to actually fund the pool.

Added.