create mintable 721 contract called NiftyVault

[cupOJoseph]

• Mintable function can be called by SafeManager to create a new safe and mints a new NFT with SAFEid = nft id
• set SafeManager address during deployment once
• update deployment scripts to set SafeManager address
• permissioned setter for updating SafeManager address that can only be updated by the DAO address
• import openzeppelin 721
• added to Proxy Registry and renaming the contract Vault721

testing

• minting can only be called by authorized address

[daopunk]

mint = create safe

[daopunk]

pushed to arby branch

[cupOJoseph]

closed in #11