[ Bugfix ] - Fix export to artemis

See merge request sharing/codeability-sharing-platform!73

New statistic: Number of times exercise has been added to watchlist

See merge request sharing/codeability-sharing-platform!72

Add null checks

See merge request sharing/codeability-sharing-platform!68

Authorization Management replaced by a solution without sessions

Komplexere Berechtigungen

See merge request sharing/codeability-sharing-platform!69

Improvement/adapt import to new artemis export

See merge request sharing/codeability-sharing-platform!70

wrote query to sum up the number of watchlist entries for an exercise id, then wrote the test and merged development into my branch

# Conflicts:
#	src/main/webapp/i18n/de/exercise.json
#	src/main/webapp/i18n/en/exercise.json

Fix duplicate "help" entry

See merge request sharing/codeability-sharing-platform!65

Resolve "Collections wieder Leben einhauchen"

See merge request sharing/codeability-sharing-platform!64

# Conflicts:
#	src/main/java/at/ac/uibk/gitsearch/es/model/ArtemisExerciseInfo.java
#	src/main/java/at/ac/uibk/gitsearch/es/model/ExerciseInfo.java
#	src/main/webapp/app/exercise/import/exercise-import.component.html
#	src/main/webapp/app/exercise/import/exercise-import.component.ts
#	src/main/webapp/app/shared/model/artemis-exercise-info.model.ts
#	src/main/webapp/app/shared/model/exercise.model.ts

This is no longer an enum, so we cannot reliably
translate it.