Prepare blockchain token minting

[mederic-p]

Issue/Task Number: 1149
Closes #1149

Overview

This PR adds the required blockchain interaction calls for token minting.

Changes

Add the following call to EthBlockchain.Adapter

• :mint_erc20
• :lock_erc20
• :is_erc20_locked

Usage

Create an unlocked token using swagger's token.deploy_erc20 call.

Then in an iex -S mix (replace the addresses with your own):

Mint the token:

EthBlockchain.Adapter.call({:mint_erc20, %{contract_address: "0x624f6081473204343f43b37a910b1f79ecc2be69", from: "0x811ae0a85d3f86824da3abe49a2407ea55a8b053", amount: 100}}, [])

Check if the token is locked (shouldn't be at this point):

EthBlockchain.Adapter.call({:is_erc20_locked, %{contract_address: "0x624f6081473204343f43b37a910b1f79ecc2be69"}}, [])

Lock the token (prevent further minting):

EthBlockchain.Adapter.call({:lock_erc20, %{contract_address: "0x624f6081473204343f43b37a910b1f79ecc2be69", from: "0x811ae0a85d3f86824da3abe49a2407ea55a8b053"}}, [])      

Check again if the token is locked (should be at this point):

EthBlockchain.Adapter.call({:is_erc20_locked, %{contract_address: "0x624f6081473204343f43b37a910b1f79ecc2be69"}}, [])

[unnawut]

LGTM with minor comments