Implement CoreData persistent store

[w-i-n-s]

Original task:

Implementing multi-wallet. Should use Core Data as ORM. Only unique entropyMask can stay in defaults for whole app. For each wallet:
- which network (testnet, mainnet, and later also Signet)
- the threshold (how many signatures are required)
- information about each co-signer: their xpub and derivation path
- a list of pre-derived addresses

[Sjors]

This is done!