User authentication token

[LucasSNSantos]

Feature

Simple login method with email and password.

• Create a new User with email and password. Email is the key.
• Validate the Token when sent to the server

[RiccardoCafa]

Changing label to backend since this is done on server-side, not on client. I will work on that so we can work on a more definitive version for the other backend part.

I'll implement using google Third Party authentication, we can add more types later on.

[RiccardoCafa]

I've changed my mind, I think it's better for the development to start with a simple email and password login. Later on we improve the authentication.