Add ability to query all credit holders with pagination

[ryanchristo]

Summary

The Registry Interface will eventually have a page that lists all credit holders with the ability to sort the credit holders by tradable, retired, and escrowed amounts. There is currently no way to query all credit holders using regen-ledger.

Problem Definition

A user should be able to query all credit holders with pagination.

Proposal

Add the ability to query all credit holders with pagination and consider indexes for each amount type.

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