Add support for lazy loading of nodes in JoustTree
|Reported by:||Nicklas Nordborg||Owned by:||Nicklas Nordborg|
The JoustTree component is used to generate various overviews that are displayed as trees in the web client. The current implementation requires that all nodes are defined at the same time the tree is created. This results in performance problems in some situations since the tree can be rather large in some cases. See #1240 and #1241.