Break out internal product properties into a more generic polymorphic internal properties model.

Initial commit that applies internal properties to product and variants. Does not support adding/updating/deleting internal properties.

readme update

wip sharing with richard

more work to get variant internal properties working

Fix add property button javascript

Changed to make the naming consistent

Added TODO for Chris

more changes to support internal properties

* positioning now works
* button customized to variant or product
* more tests

rename per rails g convention

rename per rails g convention

fixed readme

move generator to new naming convention

rename

adjust test

incorporate code review feedback from richard

fix for helpers