add flix and test generic transactions

[joshuahannan]

Closes: #222

Description

• Adds assertions to generic_transfer_with_address to make sure the vault is the correct type
• Added a test with MaliciousNFT to test the transaction. MaliciousNFT is the same as ExampleNFT, but returns the ExampleNFT paths in the NFTCollectionData view instead of its own paths.
• Adds FLIX to the main generic transactions
• Updates comments in NonFungibleToken
• adds generic_transfer_with_address_and_type since some NFTs might not have the type NFT

I can't think of any other assertions to put in the transactions, but I am open to suggestions

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For contributor use:

• Targeted PR against master branch
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the standards mentioned here.
• Updated relevant documentation
• Re-reviewed Files changed in the Github PR explorer
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[sisyphusSmiling]

Nice additions!