Improvements to support TrustBloc wallet functionality

[DRK3]

Improvements to be made to support wallet.

Features

• Support multiple key-value attribute pairs for the query endpoint (Update queries to support having multiple key-value pairs per index #118)
• Pagination support (Add pagination support for queries #168). Note: the spec is missing pagination syntax - it will need to be added (Pagination syntax for queries decentralized-identity/edv-spec#14)
• Support for sort options on queries (Support sort options on queries #231). Note: missing from spec, other issues with this due to encrypted nature of EDVs

Performance Optimization

• When using MongoDB, we can reduce number of calls to the database and the number of documents created by eliminating the need for "mapping documents". This will require a redesign... it may require a custom storage implementation rather than using the one in aries-framework-go (Figure out better way to manage encrypted indexes than using the tag mapping documents #218)