A lot of changes :D

1) Deleted the users address. A user has only Country
2) Modified the User: The user now has sent messages and recieved
messaged. The Password property was renamed to AuthCode(authentication
code/sha1 encrypted password). Added a property SessionKey (a string key
for the current session).
3) Fixed the foreign keys with the messages via Fluent Mapping API
4) Modified the DbContext and UnitOfWork: There are no more Addresses
and Cities Entity Sets
5) Added BaseApiController that has a method that performs operation and
handles the exception from the operation.
6) Added UserRegisterModel and UserLoggedModel