Refactor the habit creation controller to make use of MVVM

[TiagoMaiaL]

Apply the MVVM pattern initially to the habit creation view controller. Make it lighter, more testable, and more reusable. Other controllers will come in the next weeks.

• [ ] Write the HabitHandlerViewModel
• [ ] Make use of it in the HabitCreationViewController
• [ ] Turn the static tableView into a dynamic one