Changes

[sto8, tsk36] API method to attend an event implemented, but not
finished

Problems with testGetCreatedEvents.

Conflict with unattendEventTest

[sto21-task53] Browse Event by id
The getEvent method has been created in the EventResource.java class of
the REST layer and the test has also been created to test the operation
of the new method.

[sto17-tsk49] Method that allows you to update an event to the organizer
A method has been created so that the organizer of an event can modify
that event. Its operation has also been checked. The file
"user-update-event-title.xml" was modified because it had an error.

[sto21-tsk52] Adds create event rest api
This commit adds the post method for creating an event to the rest api. 
For this, a test event constructor has been created for ignoring 
validations. Besides, the IllegalArgumentExceptionMapper was created and 
authorized user was unified.

[sto8, tsk36] API method to attend an event implemented, but not
finished

[sto8,tsk35] Implemented rest method that returns a list with the events
created by the logged user. Tests already created. [sto8,tsk36]
Implemented rest method that allows the logged user to attend an event.
Tests already created. Modified EventDataset, UnattendEvent, and
datasets (user-precancel-event.xml and user-cancel-event.xml).

[sto8,tsk35] Implemented rest method that returns a list with the events
created by the logged user. Tests already created. [sto8,tsk36]
Implemented rest method that allows the logged user to attend an event.
Tests already created. Modified EventDataset, UnattendEvent, and
datasets (user-precancel-event.xml and user-cancel-event.xml).