[feat] #111: Send multiple outputs: change click options:

* Breaking change: Rename `--output` option to `--recipient`
* Add extra small options to ease passing multiple amounts and recipients:
  * `-a/--amount`
  * `-d/--amountUD`
  * `-r/--recipient`
* Add possibility to pass multiple options:
  * Breaking change: recipients public keys are no longer `:` separated: `-r A -r B`
* Store the options in variables names in plural for preciseness
* Fix: Handle the case when no option specifying the amount is passed
* Restrict `--allSources` option to a single recipient, case not handle for now
* Extend tests with two upper checks
* Improve help