Optimizacion del metodo de busqueda de una venta especifica.
Es utiliza el metodo find del entity manager.
Merge remote-tracking branch 'remotes/origin/master2' into augusto
Merge branches 'augusto' and 'master2' of https://github.com/Pweb-fpuna/tarea2 into augusto

Conflicts:
	src/conf/persistence.xml
Manejo de excepciones mejorado.
Merge branch 'master2' of https://github.com/Pweb-fpuna/tarea2 into augusto