first pass at static tab editing. Doesn't yet support drag/drop as well as new tab creation, which needs to modify the policy on the course

implement static tabs. rejigger .tar.gz import to do the re-namespacing as a post-processing step as we need to retain the original url_name during the import. Also, migrate the presentation tier to use module_render.py::get_module() to better unify HTML'ifying stuff

- Piotr requested this.  Hopefully it doesn't break anything, but we should run it by the content fellows before merging.

* change references and tests
* add staff/non-staff display
* added is_staff to ModuleSystem

* Also get rid of lazy loading of metadata and definition

The basic form has been fleshed out. Things still to do:
1) Extend get_course interface to the rest of modulestore
2) Make courses actually load
3) Make org/course/maybe others metadata attributes for course_module (see xml_module), so
that they are loaded/saved on import/export to xml

Begin using a Keystore for XML parsing. Still broken: sequence icons, custom tags, problems, video js

Remove semantically meaningless sections from course.xml by moving their attributes onto the contained element. If there is more than one contained element, turn the section into a sequence. Also handles includes

Also:
Render all XModuleDescriptors in the cms the same way
Default them to editing raw xml, if there is no specific module for them

Add categories and XModuleDescriptors for all module types that are used at the top level of a course

Add categories and XModuleDescriptors for all module types that are used at the top level of a course