- I added them when playing with input types, but never merged them in

add to existing test cases to exercise the 'course extras as modules' work in the CMS import. Also add to the existing 'full' test data collection to include policy, tabs, etc.

* was going to use to test duplicated content, but we're not supporting that for now

* 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

* with backcompat location /grading_policy.json

* still backcompat with old mode

* apply policy per-course, even if multiple courses share course and org fields
* keep descriptors separate in xml store, so that if two such courses
  change the same module in different ways, it works.  Such edits will need to
  merged on CMS import...
* add get_instance(course_id, location) method to replace get_item(location).
  Update all the call sites
* tests, including a 2nd toy course with same course and org.

* 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

- add 'type' and 'points' to capa_module metadata
- replace old 'title' tag with display_name

TODO:
* need unique slugs for errors so they don't overwrite each other on export.
  - try to preserve origin slug.  If not possible, generate random one.

* figure out what metadata to strip.  e.g.
 ({'data': '<problem><p><h1>Finger Exercise 1...'},
    {'data': '<problem points="1" type="lecture"><p><h1>Finger Exercise 1...'},
    False)
  - where did points and type come from?  Do we want them there?


* separate broken and non-broken test courses

* add course and org to full/course.xml
* fix error path in clean_xml script
* commit rakefile change needed by c5334f150c

* Add extra nested html file
* add a start date

* More tests for mongo modulestore, including tweaks to test files
* add location_to_id method to CourseDescriptors
* Implement path_to_location method in mongo.py
  - TODO: does not handle position in sequences yet.
* fix bug in jump_to view.

* Clean up test data for simple, toy courses
* clean up test_mongo.py
* write initial test for path_to_location
* hook up view to use path_to_location

Next: actually implement it :)

* fix up toy course to match current format
* fix github sync test that referred to toy course

* change custom tags in test/data/full to new single-tag format
* fix broken file references
* fix argument to import_from_xml
* error_handler fix in mongo.py in next commit

Add tests for the edit page for the toy course, and make sure that exporting to github sets up the git repo properly