Use uint64 to track rclimit

[youkaicountry]

Resolves #163

Brief description

Checklist

• I have built this pull request locally
• I have ran the unit tests locally
• I have manually tested this pull request
• I have reviewed my pull request
• I have added any relevant tests

Demonstration

 🔓 > tkoin.balance_of
1000000 KOIN

🔓 > rclimit
Current rc limit: 100% (1000000)

🔓 > rclimit 25%
Set rc limit to 25%

🔓 > rclimit
Current rc limit: 25% (250000)

🔓 > session begin
Began transaction session

🔓 📄 > tkoin.transfer 186zJQa3hjXx3zTxhYYJwrYjvntYxUjFA7 10
Transferring 10 KOIN to 186zJQa3hjXx3zTxhYYJwrYjvntYxUjFA7
Adding operation to transaction session

🔓 📄 > disconnect
Disconnected

🚫 🔓 📄 > rclimit 100
Set rc limit to 100

🚫 🔓 📄 > session submit
JSON:
{
  "id": "EiC1h99MizJ9gGLIX6Gb27/FHeHKGpM3iSvDyGFEesH47A==",
  "header": {
    "chain_id": "aaaaaaaa",
    "rc_limit": 10000000000,
    "nonce": "KGQ=",
    "operation_merkle_root": "EiAjZX5OX28FvED8un2QPjx6/MZXWpVxoydusbmd2ITd3w==",
    "payer": "AJJ3kv38SxPn5+TzlAsxGtTNhhmcdFk5Ug=="
  },
  "operations": [
    {
      "Op": {
        "CallContract": {
          "contract_id": "AFseYdNyWbnC2Zv0F/WS4Ld3JRZdJIi+RQ==",
          "entry_point": 670398154,
          "args": "ChkAkneS/fxLE+fn5POUCzEa1M2GGZx0WTlSEhkATerKwbchYzQyDN55HkNXF11J0SqbTALoGICU69wD"
        }
      }
    }
  ],
  "signatures": [
    "HyvPTLP1cTRPw6zHZp/KZGPq5KOo85hA9f6MM+ClwYTLQ4g6SaX4StbcSnLcV2gHSZ3W5aezR1WEaFdKluBGFVs="
  ]
}