[#45] Add field password with validations and unit tests.

Add field password.
Add validation of type, presence and uniqueness of email.
Add validation of type, presence and confirmation of password.
[#45] Add format validation for email and unit test.
[#45] Clean-up: fix indentation.
Merge pull request #1 from gotar/user-model

[#45] User model with validations and unit tests.