Mintlayer Trezor Improvements

[OBorce]

Improvements:

• New dialog for token total confirmation (also see Feature/mintlayer pk #1 (comment))

• Support marking of change outputs like BTC (also see Feature/mintlayer pk #1 (comment))

• Add support for returning the serialized transaction like BTC.
  (Note that we don't really need this for our core wallet, but if some other wallet integrates Mintlayer support, it may be useful for them to be able to just take the resulting tx and submit it).

• We should probably refine our output confirmation dialog.
  At this moment, our confirm_output function calls layouts.confirm_output if the output has an associated amount, and layouts.confirm_text if it doesn't. This leads to some inconsistencies in how the outputs are presented, e.g. in one case the output index is displayed in the title, and in the other case it's just "Confirm details". It's better to unify this.
  Note: consider implementing our confirm_output function separately for each type of ui, like they do it for confirm_ethereum_tx.