dashpay
add replacement method for removed insight api `getUTXOS` fast balance retrieval of external addresses
After removal of the insight api getUTXO method to retrieve the balance of an external address one must use a centralized insight server or use the low level subscribeToTransactionsWithProofs method which requires tracking the transaction and calculating the UTXOs and is slow.
Consider a user tipping a tweet, they would send some dash to an address associated with the tweet. The address is publicly known and associated with the ownerId. In the UI and for sorting by different metrics, we need to know how many tips were received by this address. A highlevel function to quickly and efficiently retrieve the address balance, or a masternode signed index of a snapshot of the address balance at a certain time are required to provide a usable experience for the users looking, sorting and filtering hundreds to thousands of tweets.
PR dashevo/wallet-lib#290 has been merged. It offers an initial support for the requested need. However, as the full request here is not adressed yet, I'm letting this open. We do track this task internally.
