v2.2.0 Secured Auctions + USDC distribution

• Support for private auctions. Bidders of a private auction must obtain an authorization from a central service.
• Distribute the shares of joint accounts directly in USDC.
• [BREAKING] The event StartAuction changed. Indexers must support both the old and new versions.

PRs

• signature verifier impl by @AlekseiMisyukevich in #52
• erc20 share transfer impl by @AlekseiMisyukevich in #54
• README: How to upgrade by @naure in #58
• (un)secured auctions by @AlekseiMisyukevich in #57
• feature/FREEP-562-aurel: setURI function by @naure in #61
• prepare-2.2.0: restore state of 2.0.0 deployment by @naure in #62
• fix/authorizer-init: remove the need for initialization of EIP712 by @naure in #63
• FREEP-562: Deploy v2.2.0 with setURI by @naure in #64
• Fix/eip712 layout by @naure in #65

Full Changelog: v2.0.0...v2.2.0