Remade of deleted files
Database-Java fix
Added queries to a lot of classes: see change log
Finalized queriesto Skill and field of study and started working on nested comments
idea changed
idea change
Addidea, Deleteidea and getIdea methoden toegevoegt. 
en instantievariabelen toegevoegt voor codebesparing
Concreteidea kleine aanpassingen / fixes
push
Merged database into Tests