wallettemplate WIP: improve key derivation spinner, remove wallet tag

[msgilligan]

Progress meter no longer uses a fixed, estimated duration. Instead it uses a fixed, maximum-expected duration (set to 10 seconds) but will complete when the actual derivation completes.

This allows us to remove the saving of the estimated duration in a TAG field added to the ProtoBuf wallet saved data.

• WalletApplication: remove calculation of estimated time upon startup
• KeyDerivationTasks: Progress meter completes when derivation completes
• WalletPasswordController: Remove code to update and save (as a TAG) estimated time
• WalletSetPasswordController: Remove code to estimate and set derivation time