NFT Dapp where people can mint Brainnest's NFTs, maxSupply=50
maxSupply is setup in the constructor(50)
there are privateMint and publicMint(publicMint is true since the begining)
privateMint(payable) --> only users with allowance(mapping) can mint sending 0,001 ether
publicMint(payable) --> any user can mint sending 0,000001 ether
onlyOwner can set the allowance to any wallet
onlyOwner can open/close the privateMint and publicMint
withdraw balance of the contract - onlyOwner