Rework transaction functions (Part 4)

Follows #184 (closed)

• tx: sources retrieved twice in get_amount_from_pubkey() and get_sources()
• rename get_amount_from_pubkey() to get_balance()
• handle --allSources with several recipients pubkeys: balance divided among recipients pubkeys
• e745bb95: Refactor the one-liner condition
  • move to transaction_confirmation()?
• Improve variable and function naming:
  • issuers –> issuer: No, there could be many issuers, but it’s not implemented yet
  • issuers should be a list, even if it contains only one element for now.
  • camelize consistency for outputBackChange in code as a variable and as an option. Rename to RecipientBackChange
  • output* —> recipient*:
    • in the code
    • in the cli: pass recipient pubkeys as arguments to be able to specify many without the : split
  • curentUnitBase –> cur*r*entUnitBase
  • amount –> balance
• #193: Dataclass to access units in unit or in cent format
• #119 (closed) Simplify confirmation message as now there is a recap chart before sending a transaction
• rework, refactor this whole code