Unify all CRUD forms

[Mehonoshin]

At the moment some entities have new, create, edit, update forms which basically have the same form definition.
Let's unify them by extracting shared markup to a separate _form.html.haml template for each entity.

Be careful, this task requires detailed manual testing, including cases when submitted form was invalid. In this case it should display a form with filled fields and display validation errors on the page.