added a new curated exercise by Potsdam University

mc_backend/tests.py

mc_frontend/README.md

mc_frontend/src/app/app-routing.module.ts

mc_frontend/src/app/app.component.spec.ts

mc_frontend/src/app/corpus.service.spec.ts

mc_frontend/src/app/corpus.service.ts

mc_frontend/src/app/embed/embed.page.spec.ts

mc_frontend/src/app/embed/embed.page.ts

mc_frontend/src/app/exercise.service.spec.ts

mc_frontend/src/app/exercise.service.ts

mc_frontend/src/app/exercise/exercise.page.html

mc_frontend/src/app/exercise/exercise.page.spec.ts

mc_frontend/src/app/exercise/exercise.page.ts

mc_frontend/src/app/helper.service.spec.ts

mc_frontend/src/app/helper.service.ts

mc_frontend/src/app/home/home.page.html

mc_frontend/src/app/models/enum.ts

mc_frontend/src/app/models/exerciseParams.ts

mc_frontend/src/app/models/language.ts

mc_frontend/src/app/preview/preview.page.spec.ts