Add a weighted_popularity contest that takes into account variable weights on different NFTs

[andrew-octopus]

Use Case: (For instance, suppose that being a Study Session Speaker counts 10x as much as earning an NFT Fundamentals NFT.) The weighted_popularity_contest method would take into account the weights that each NFT has earned, and count votes according to these weights.

Args:

• sample, a list of Voters with vote attribute assigned.
• weights, a dictionary, assigning a numerical value to each NFT.

Return:

• winner, the candidate who won the contest.