This reverts commit 72c9a602.

into development and additional clean up

Conflicts:
	src/main/java/at/ac/uibk/gitsearch/service/GitlabService.java
	src/main/webapp/app/app-routing.module.ts
	src/main/webapp/app/exercise/service/exercise.service.ts
	src/main/webapp/app/search/search-input/search-input.component.ts
	src/main/webapp/app/shared/model/exercise.model.ts

Resolve "editorial pages"

See merge request sharing/codeability-sharing-platform!59

# Conflicts:
#   src/main/resources/.h2.server.properties
#   src/main/webapp/app/exercise/service/exercise.service.ts

Resolves #162 and #171

See merge request sharing/codeability-sharing-platform!58

refactored statistics so that they are loaded by the statistics service and then resolved the collections bug

added security check that checks if user can see the exercise he is liking and added an index on exercise_id to likes table