Made sure files in core/ and tools/ have a proper Godot license header
when written by us. Also renamed aabb.{cpp,h} and object_type_db.{cpp,h}
to rect3.{cpp,h} and class_db.{cpp,h} respectively.
Also added a proper header to core/io/base64.{c,h} after clarifying
the licensing with the original author (public domain).
-Added constructor nodes, specialized and conversion ones.
-Cleaned up how unconnected input default values are shown and edited (much cleaner)
-Dragging scene nodes into graph makes a call dialog appear by deault
-Dragging properties into graph is set by default, not get
-fixed dragging internal functions into graph
