GnumarusSceneTreeViewButtons

Adds new buttons to the scene tree view.

Currently three new buttons are added

1. Editor Comment: Every node that has a non empty editor_comment property will show up a sticky note icon. When pressed, this will select that node and open up the editor_description edit popup
2. Incomming Connections: Every node that has one or more incoming connections will show up a "hearing ear" icon. When pressed, this will open a popup listing all current incomming connections to that node.
3. Metadata: Every node that has one or more metadata entries show up a "sandwich" icon (three dashes). When pressed, this will open a popup listing the current metadata on that node.