This commit adds the new resource UsersResource (/users) with a simple
functionality: retrieving the data of an user. This functionality
requires knowing the login of the user that is performing the request.
In this regard, this commit is an example of how this information can be
retrieved and how to test a resource that requires knowing the login of
an user.

The tests classes have been simplified by delegating some of the
functions in the test classes to external utility classes. For example,
a PeopleDataset has been added to manage the dataset or the
IsEqualToEntity Hamcrest matcher has been added to simplify entity
comparisons.

In addition, a PersonUnitTest class has been added to test the Person
entity.