Perform Coin Selection on the available UTxO (with fee adjustment) (cf: Kernel/CoinSelection)

• Generate change address
• Sign transactions with corresponding private keys
• No more grouping policy
• Funds are taken within the wallet (regardless of the account structure)
• A transaction may have the following metadata:
  • A unique identifier
  • A depth (a.k.a "number of confirmations")
  • A status: pending vs in-ledger vs invalidated (instead of: "applying", "inNewestBlocks", "persisted", "wontApply", "creating")
  • A total amount
  • A direction (outgoing vs incoming)
  • A timestamp
  • Absolute (from genesis) slot number & block number the transaction was inserted

Keep in mind that in a near future, we do want to allow signing transaction off-band (by another software), so signing shouldn't be tightly coupled to transaction submission.