Issue #79: Add delete form feature.

form-creator-database

src/api/controllers/form.spec.ts

src/api/controllers/form.ts

src/api/controllers/user.ts

src/core/form.ts

src/core/formUpdate.ts

src/utils/answerQueryBuilder.ts

src/utils/dbHandler.spec.ts

src/utils/diffHandler.ts

src/utils/formQueryBuilder.ts

src/utils/optHandler.ts

test/scenario.ts