updateable contracts part 1

[Westlad]

DO NOT RELY ON contract-update.md for reviewing this PR. The pattern used here is quite different. Instead, read the Openzeppelin Upgades link below. We'll update the documentation when these changes are finalised.

This PR deploys proxied contracts that can be upgraded. To keep PRs small, this is the first of (probably) two PRs. This PR simply adds upgradable contracts, it does not provide any means to carry out an upgrade; that will follow in a second PR.

The PR leans heavily on Openzepplin's Upgrades library. Nevertheless, some changes are required to make contracts upgradeable. This is mainly:

• proxies are oblivious to constructors and thus constructors are replaced by initialize() functions (note the US spelling or expect hard to find bugs). The initializer modifier ensures they can only be called once.
• .transfer no longer works because it has heavily restricted gas to prevent reentrancy. We replace it with .call. This increases the risk of reentrancy attacks and so functions use a checks-effects-interactions pattern normally, but all are additionally protected by the Openzepplin RentrancyGuard modifier which prevents a modified function being called reenetrantly in any case.

Testing is as normal but you will need to run ./setup-nightfall to incorporate changes to the packages used. Note that the contracts are actually being called transparently through their proxies in the tests.

[signorecello]

Great stuff! I would just remove the console.logs used for debugging, though

[ChaitanyaKonda]

This PR looks good.

To understand what I should review, I relied on the plugin documentation link you provided.
I presume the following changes as suggested in upgrade plugin will come in the next PR as suggested in your description.

The PR leans heavily on Openzepplin's Upgrades library. Nevertheless, some changes are required to make contracts upgradeable.

• Config.sol defining initial values for field declarations
• Stateful.sol to initialise state.sol inside initialize()
• Adding Upgradeable suffix to contract names
• Utils.sol defining initial values for field declarations