Changes

tsk42 Fixes of the competition service
Adds the check that the recovered objects have not been previously
deleted. Also in the search by name and description, it is allowed that
the description is not exactly the same as the one introduced. Also
eliminates some unnecessary checks such as the type of sport that is
null since this option can't be produced by being an enumerated, or user
verification in the creation of the competition.
Complete javadoc and change some error message to better specify the
error produced.