Add custom javascript missing from newforms-admin (js field missing)

[mrts]

Old admin interface had a way to add custom javascript to models in admin:

class MyModel(models.Model):
   ...
   class Admin:
      js = [ 'foo' ]

This functionality was missing, the attached patch adds the same functionality back:

class MyModel(models.Model):
   ...

class MyModelAdmin(admin.ModelAdmin):
   ...
   js = [ 'foo' ]

It's a simple patch and should generally be ready for checkin.

[mrts]

Add missing custom js handling

[jkocherhans]

Javascript in the admin is taken care of by the new inner Media class in newforms-admin. It's even ​documented, albeit hard to know about if you haven't been watching the branch for a long time. :)