This fixes the following tests(T stands for toy, F stands for factory made):
T import_textbook_as_content_element (needed to add a textbook to toy)
F static_tab_reordering
T import polls (needed to add a poll to toy)
T xlint_fails
F delete
T about_overrides (needed to add an about override to toy)
F remove_hide_progress_tab
* New format: {tag}://{org}/{course}/{category}/{name}[@{revision}]
* Updated tests, code
* Added test chapter with : in url_name in toy course
* added test html page with : in url_name
* added a note to docs
* course roots live in roots/{url_name}.xml
- one is linked from course.xml
* policies live in policies/url_name.json
- loaded based on course url_name
* Updated to pass policy through into xml parsing, so it takes effect
before descriptor constructors are called.
* Update toy test course to new structure, fix up tests
