Insertion points with select

Check it out, @shailen and @Sfshaza.

Staged at:
https://github.com/dart-lang/polymer-dart-snippets/tree/insertion_points_with_select/web/insertion_points/creating_insertion_points_using_the_select_attribute#creating-insertion-points-using-the-select-attribute
This is fine for a single sample, but just about every sample will have this file. Do you still want to describe what each file does?