Complex storage queries (Wallet Query Language (WQL))

[karimStekelenburg]

For some use cases it's currently required to query the StorageService multiple times in a row. This would not be necesarry if the StorageService would expose an API that allows for complex queries that include $and, $or and $not clauses.

We should implement the Wallet Query Language (WQL) as specified by Indy doc 011.

[berendsliedrecht]

Do you think we should just allow a WQL string or should we create a builder for this? Would be quite a nice feature to have, and with a builder we could also expose it publicly.