Make InteractiveComponents (images) support onClick

Add onClick handler to the base InteractiveComponent
class, which is currently only extended by ImageController.

[#44616109]
Support image urls starting with "/resources"

Previously image urls were either absolute (http://..)
or were relative to the model url.

This change allows urls of the form "/resources" to be
used without changes (i.e. making them relative to the
lab url) because it will be common to refer to images
in the main resources folder.
Make credits link the CC logo

[#44616109]