Added NftId class, fixed some bugs

[LukeBair]

Added NftId Class

Added a nft_id.py file that contains a NftId class, the NftId class has the following variables and functions:

• tokenId and serialNumber
• init()
• is_valid(), checks to see if the NftId is in a valid format
• from_proto()
• to_proto()
• from_string()
• str()
• repr()
• eq()
  The NftId class has the "@dataclass" annotation, and autogenerates the repr(), init(), and eq() functions, it also freezes variables to make them immutable.

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Modified TokenId Class

Added a few functions and type safety to the TokenId class (in token_id.py), functions added:

• is_valid(), checks to see if the TokenId is in a valid format
• repr()
• eq()
• hash(), there was an error that required TokenId to be hashable
  The TokenId class now has the "@dataclass" annotation, and autogenerates the repr(), init(), and eq() functions, it also freezes variables to make them immutable.

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Misc

Added nft_id_test() which checks to make sure that incorrect values are found and correct exceptions raised when they should.

Fixed a bug in test_token_dissociate_transaction.py which was causing pytest to fail due to an invalid path.