Added foreign key with onDelete clause on user to label and criterion relationships

FEA: ItEr77S15FilteringEnhancements
Reverted unnecesary changes on Label and Criterion save operations to clear removed entities

Since the "foreign key" constraint with onDelete parameter introduced into liquibase is handling
at database level the integrity, the external operations to clean the setting values are not longer
needed.

FEA: ItEr77S15FilteringEnhancements
Moved session manipulation calls to the refactored class

FEA: ItEr77S15FilteringEnhancements