Fix scss errors

There were a couple of SCSS errors that I found with different logging settings.  These were both because the respective stylesheets didn't include widgy_common.scss.

django.fusionbox.scss was trying to use `%loading`, but it didn't include widgy_common.  I deleted all of the duplicate stuff from django.fusionbox.scss.

html.admin.scss was trying to use `@include html`, but it didn't include widgy_common.