refactor: Refactor module error handling

[hacheigriega]

Explanation of Changes

This PR improves consistency of overall error handling in module code (excluding CLI code, tests, and proto-generated code).

• Follow the Cosmos error handling instrucitons https://docs.cosmos.network/main/build/building-modules/errors
• Avoid using fmt.Errorf() to create or wrap errors. Instead, create error types in errors.go in the corresponding module's types package.
• Avoid stringifying error objects because that prevents access to the source error.

Closes #331 - Logging strategy in module code is already uniform.