Query PoE contract addresses from contracts

[alpe]

Add custom query to return address by type
Quick version of #129 limited to return PoE contract addresses

No need to restrict access to privileged contracts

Background:

Queries are defined in wasmvm QueryRequest type and bindings for the contracts.
They are executed within wasmd's plugin handler that has access to state and native modules to runs them.

In tgrade we extend the basic functionality for PoE or other new functionality via the custom message type.
The new handlers can be setup in app/wasm.go.
We don't have a custom-type handler yet but I hope you find some inspiration in the default wasmd handlers.

Not related to this task but as an example for custom messages that I have implemented: twasm/handler_plugin