Build/flattener

[tcrosado]

Description

Add script to flatten solidity files to be verified by Etherscan

Motivation and Context

To use the script just type:
Flattener.py origin.sol destination.sol
Where origin is the starting point or the contract code to add the the Etherscan and destination.sol is the flattened contract code with all the dependencies.

Currently the code tries to order the dependencies correctly just by ordering the contracts based on the number of dependencies of each contract, however further improvements can be made.

How Has This Been Tested?

Screenshots (if appropriate):

Checklist:

• You have followed our contributing guidelines
• double-check your branch is based on dev and targets dev
• Pull request has tests (at least 80% coverage)
• Code is well-commented, linted and follows project conventions
• Documentation is updated (if necessary)
• Description explains the issue/use-case resolved and auto-closes related issues