Milestone 10: Port openzeppelin to Parity Substrate

[xermicus]

OpenZeppelin is a popular library for Solidity developers, however it uses many eth-centric constructs. Make a fork of the library which can work on Substrate using Solang with as much functionality, as possible, preserved.

This feature should have tests at

https://github.com/hyperledger-labs/solang/tree/main/integration/substrate

Success means that a pull request has had all its review comments addressed and it is merged.