global: refactor DTO structure

[BrunoRosendo]

Until a while ago, all the DTOs we had were a direct mapping between DTO and model, so we had a Dto class with useful methods like create() and update(). However, we quickly realized we need more than that kind of DTO (see discussion in #54 (comment)). The result was a few DTOs residing alongside the controller classes, which is not ideal.

The discussion above proposes the following solution:

dto/
     model/
     auth/
     otherSemanticUseCase/

This dto package should either reside in the global scope of the application or inside the controller package, I'll leave that to discussion. It'd also be nice to consider cases of model DTOs that need more fields than the respective model's fields (e.g. creating a project with a list of account IDs to be used as its team).