Ref: #3880 (comment)

We now have three router logic:

Tx Router: https://github.com/cosmos/cosmos-sdk/blob/develop/baseapp/router.go
Query Router: https://github.com/cosmos/cosmos-sdk/blob/develop/baseapp/queryrouter.go
Proposal Handler: (PR not merged yet)

We need to abstract out this logic, we expect the number of multipurpose modules(like governance proposal) will increase. Two possible implementations are go generate and reflect(https://golang.org/pkg/reflect/#Value.Call). AFAIK go generate is recommended to avoid in our codebase, and reflection is inefficient. Is there a better way to improve?