Modify the theme's Apply button link on runtime for grad programs

[bjcfuller]

The Apply button in the theme defaults to undergraduate admission. That's fine unless the user is browsing a graduate program, in which case the button should go to graduate admission.

If the theme has a hook for that button, the program finder can modify that link at runtime to point to the graduate school, based on whether the page served is for a graduate program or not.

[bjcfuller]

@johnpennypacker have anything to add?

[johnpennypacker]

I like the hook approach. :solid:

I wonder how far we want to take it... do we each link in the action bar? the links themselves? Probably best to keep it simple with the hook you propose until additional needs emerge.