Revert "cambio clases Asignatura y Alumnos"

This reverts commit 0d2d1a6e232b32dd87c6f01065bbad68f9e0eb11.
Revert "Revert "cambio clases Asignatura y Alumnos""

This reverts commit 7f956d10f1ede1533faa631289e9170508f0e6a2.
cambios de clases