add new project for a tree graph display control
Inspector: add ability to show both lineages
TGC: add ITreeNode interface and basic abstract implementation
add DisplayGrid class to position tree nodes
begin implementing the TreeGraphControl

Create class, implement node positioning algorithm.
TGC: remove event listener on root node
TGC: implement painting
TGC: add HitTest(PointF)
TGC: change namespace to TGC
TreeNodeBase: add re-raising of DescendantsChanged event
TGC: improve layout algorithm
TGC: add visibility to ITreeNode
add visiblity handling to TreeGraphControl itself
refactor Inspector: Lineality enum
add GenealogyTreeControl to inspector (subclass of TGC)
add functionality to GenealogyTreeControl context menu
Inspector: add TreeWindow to display family tree
Inspector: open selected node in GenealogyTreeControl on Enter
minor GUI improvements
TGC: improve positioning algorithm

Positioning algorithm now produces more compact trees.
Instead of starting each new branch totally to the right
of the last, let nodes on lower levels use unoccupied
cells in columns of last branch.