Changed JSON generation for Apps, LAPPS-70
ApplicationResource works with AppInstance instead of App, LAPPS-70
Create app (post), LAPPS-70
ApplicationsResource /apps search, sort, pageing, LAPPS-70
use imgur for static placeholder images instead of lorempixel (since
lorempixel is down)
bugfix: userId is retrieved everytime now
Merge pull request #93 from learning-layers/users_resource

bugfix: userId is retrieved everytime now
fixed: documentation
Merge pull request #94 from learning-layers/docFix

fixed: documentation
Merge pull request #95 from learning-layers/rest_api

Rest api
Merge branch 'develop' into domain_model_improvements

Conflicts:
	LAPPS-backend/src/main/java/de/rwth/dbis/layers/lapps/domain/AppInstanceFacade.java
	LAPPS-backend/src/main/java/de/rwth/dbis/layers/lapps/entity/AppInstanceEntity.java