CreateCustomNode method.

Add a method for creating an instance of a custom node in the
MigrationManager.
MAGN-3360

Migrate ModelCurveFromCurveLoop by using a custom node which takes a set
of poly curves and generates model curves for each.
Update TransformOriginAndVectors migration.

Replace existing migration method which caused a lot of node barf, with
a single custom node which includes all logic for creation of a
coordinate system matching the original transform.
MAGN-3301

Migrate BoundingBoxXYZ. Migrate with custom node which generates a
cuboid and uses its bounding box.
Add three custom nodes to be used in migrations.