add service entry point to generate tar.gz file and return to caller. Use of the NamedTemporaryFile will auto cleanup.

fix up styling by reusing existing CSS class names. Also refactor some code regarding the management of static_tabs so that it's in the course as course contains references to static_tabs in the current data model

have import be a bit more flexible in terms of the packaging of the content. Allow for tar.gz names to be different from the course name. Also don't assume that the unpacking of the zip will yield a single top level root folder.