Ethereum scripts: minor improvements

[sept-en]

There are several minor improvements that need to be applied to Ethereum scripts:

1. Redundant/wrong ethers imports: Add scripts to deploy, upgrade and interact with EthErc20FastBridge #28 (comment)
2. Wrong naming in method task: Add scripts to deploy, upgrade and interact with EthErc20FastBridge #28 (comment), Add scripts to deploy, upgrade and interact with EthErc20FastBridge #28 (comment), Add scripts to deploy, upgrade and interact with EthErc20FastBridge #28 (comment)
3. Specify gasLimit in the task: Add scripts to deploy, upgrade and interact with EthErc20FastBridge #28 (comment)
4. Minor improvements: Add scripts to deploy, upgrade and interact with EthErc20FastBridge #28 (comment)
5. Missing function to verify user's whitelisting for the specific token: Add scripts to deploy, upgrade and interact with EthErc20FastBridge #28 (comment)
6. Missing script for the verification of the contract: Add scripts to deploy, upgrade and interact with EthErc20FastBridge #28 (comment)
7. Duplication of the deployment script (and missing latest updates): Add scripts to deploy, upgrade and interact with EthErc20FastBridge #28 (comment)