Changes

Tsk34 Adds a resource to find own microstories
Adds a new UserResource class and adds a new method to retrieve the
stories by a an authenticated author with all the necessaries test
classes and resources. Modifies the UserService to add a new checking to
throw an exception if the login is empty. Modifies the UserService test
class to test this modification. Modifies the web.xml to activate the
security constraints to add restrictions to find stories by a specific
author. Adds a new httpStatus to check the forbidden status.