WIP: Tests and comments on effects

client/src/app/metamodel/effects/attribute.effects.ts

client/src/app/metamodel/effects/column.effects.spec.ts

client/src/app/metamodel/effects/column.effects.ts

...src/app/metamodel/effects/criteria-family.effects.spec.ts

client/src/app/metamodel/effects/criteria-family.effects.ts

client/src/app/metamodel/effects/database.effects.spec.ts

client/src/app/metamodel/effects/database.effects.ts

.../src/app/metamodel/effects/dataset-family.effects.spec.ts

client/src/app/metamodel/effects/dataset-family.effects.ts

client/src/app/metamodel/effects/dataset.effects.spec.ts

client/src/app/metamodel/effects/dataset.effects.ts

client/src/app/metamodel/effects/group.effects.spec.ts

client/src/app/metamodel/effects/group.effects.ts

...src/app/metamodel/effects/output-category.effects.spec.ts

...t/src/app/metamodel/effects/output-family.effects.spec.ts

client/src/app/metamodel/effects/output-family.effects.ts