Introduce list-based mint method parameters

[pstehlik]

Support arbitrary number or proofs being submitted when minting an NFT.
Currently, the mint method requires each proof in its own set of parameters.

• Create a mint method that supports arbirtraty number of proofs being provided
  -- This allows to have a consistent ABI defition for any ERC721 registry - easier integration with clients
  Pseudo code

function mintMerklePlainText (
    address _to, 
    uint256 _tokenId, 
    bytes32 _documentId, 
    bytes32 _merkleRoot, 
    proofs [
      {
        bytes32[] _proof, 
        string _leafName,
        string _leafValue,
        bytes32 _leafSalt 
      } ,
      {
        bytes32[] _proof, 
        string _leafName,
        string _leafValue,
        bytes32 _leafSalt 
      } ,
      {
        bytes32[] _proof, 
        string _leafName,
        string _leafValue,
        bytes32 _leafSalt 
      } ,
....
    ]
  )