Decide on UX related to creation & spending of "dust" notes.

[nuttycom]

Shielded and transparent UTXOs with value less than 0.00005 ZEC are considered "dust" by zcash_client_backend; under ordinary circumstances they have no economic value because the fee required to spend such a UTXO is greater than the value obtained by spending the output. However, in many transactions there is the ability to "recover" such value by spending the UTXO as a grace input under ZIP 317. This circumstance presents several challenges:

• How should the requirement to pay fees affect the visible balance of the wallet? Should fees that will be required to spend existing UTXOs be automatically deducted from the top-line wallet balance?
• If a UTXO has value less than 0.00005 ZEC, how should its balance be included in the top-line balance? It's potentially possible to reclaim this nominal value as a grace input under ZIP 317, but it is not reliably possible to do so for each such input.