New feature

[samuelvanderwaal]

Adds the freeze feature with the following commands:

• freeze enable -- enables the freeze feature for a candy machine that has not started minting yet
• freeze disable -- removes the freeze feature
• thaw -- thaws a single frozen NFT if freeze rules allow it, or all NFTs from a candy machine with the --all option
• unfreeze-funds -- unlocks treasury funds if freeze rules allow it