Head and foot for object type

Let's say that I want to use filepicker.io to upload my files in the admin.  

With this update, I'd create:

1) kilt/form/_filepicker.html.erb => The filepicker field editor, but with the filepicker HTML.
2) kilt/form/_filepicker_head.html.erb => The JS code that has to be injected into the page head.
3) kilt/form/_filepicker_foot.html.erb => The JS initialization code, which will be injected at the bottom of the page.

If I wanted to do this without the update, I'd have to override the Kilt layout page, and inject the field-specific code into the head and foot.
This is the part of the PR I hate.  I bet there's a way to see if this partial exists without wrapping it in a rescue block.