Abstracted the functionality to convert onlineresources to jsonobject, which can be understood by the front end
Load alle the levels which are found by the csw query and show them in the csw panel. Not selectable yet
Add the found advanced csw node to the selected content (more precisely: find the level in the boomstructuur levels and add it to the selectedcontent)
Made function for clearing a tree. Clear tree on receiving the advanced search results