polygons and polylines
- destroy pass is override to force clean
polylines
- child model:
  - handles truthies and falsies for expressions
  - isDragging is tracked to avoid unecessary creation of polys
model-key
- if scopeProp is not a string then we bail out cause we have a value
  that is not a key
example
- issue_930_polylines-updates.html

TODO:
Port all these improvements to Polygons and have a polygons example

issue #930
changes from polylines moved to polygons
- PolygonChild model and PolygonsChild Model are virtually the same now.
- next step is a base class
polygons and polylines derrive from the same class now
issue #930
Merge pull request #932 from nmccready/issue_930_plygons_polylines_model_tracking

issue 930 polylines, polygons not tracking properties and models