Added TreeNode as supertype for classes representing a tree
Changed Ensemble to an interface
Added EmptyEnsemble
Added ConcreteEnsemble as "Ensemble"
Added reference from slice to ensembles
Updated ui to match updated datamodel
Added Drag&Drop for Ensemble Repository
Merge branch 'master' of git@github.com:Delors/Vespucci2.git
Updated to use new ConcreteEnsemble
Updated to new datamodel
Simplified parent and child checks