[Unblinding UTXO] Ability to detect and spend unblinded addresses

[i5hi]

Requires testing solutions addressed in:

Blockstream/lwk#38 (comment)

[delcin-raj]

Proposed Solution

There are 2 ways to solve this problem.

Case 1: Ability to detect and spend the UTXO

BREAKING CHANGE

This would require adding additional field blinded to the Balance struct to inform the user
whether this asset is blinded or not.

In that case user can call build_unblinded_tx function (to be implemented) to spend that unblinded asset.

Case 2: Ability to spend the UTXO but not detect it

In this case we can query the lwk for external utxos to display the unblinded UTXOs as regular balances.

If the user calls build_asset_tx function to spend any asset we would query for external utxos again and
would check whether that asset is blinded or not.
In case of blinded we would create that corresponding pset else the current implementation of pset.

But the user will NOT be able to detect the unblinded UTXO.

When going for case 1 other refactoring and cleanup could be done.
We can remove AssetId*Map* wrapper types as it is not straightforward to convert from BTreeMap to Balance.
We can rather create helper functions or methods for the Balance type to get that done.

NOTE: AssetId*Map* types are not used in any function signatures. So they are redundant.

[i5hi]

Case 1 is a more straightforward approach.

We would also want Transactions to show the unblinded tx.

[delcin-raj]

Working on it.

[delcin-raj]

#42