Form style must be uniformed

[masonlouchart]

The login-fire-form style changes when we are switching between the 3 views that are "sign-in", "sign-up" and "reset password".

• buttons not always aligned in the same way
• variable margins/padding
• variable widths

[Oupsla]

Related to #115 ?

[masonlouchart]

With this issue I really wanted to highlight the elements disposition (margin, padding, alignment, etc..) in the initial state. But I think we can solve the other one at the same time. 🍰