This changes logic to allow more missed use cases of course_image to
work properly.  The cases are:

. XML courses with the course_image attribute set
. Mongo courses that are imported without a contentstore
. Mongo courses that have course_image set but don't have a content store

It also exports default images_static_course.jpg to
images/static_course.jpg to handle a use case where a course author
uploaded an image to the default location in studio without using the
studio interface for adding course images, they then export the course, and then
import it without a contentstore

Part of STUD-91

-- Changed docstrings to use double quote.
-- More consistent naming for youtube IDs (normal_speed_id -> youtube_id_1_0).
-- Formatting changes for readability.
-- Updated test XML to expect JSON-encoded strings; prevents tests from spuriously failing.

Update XML in old video tests. This change tags like <video youtube="1.0:abcdefg"> to <video youtube_id_1_0="abcdefg".

Update XML in old video tests. This change tags like <video youtube="1.0:abcdefg"> to <video youtube_id_1_0="abcdefg".

get metadata inheritance to work with draft stores. Fix bug on .publish() method whereby inherited metadata got written to the DB as 'own-metadata'. Change filter in mako_module.py to return list of own-metadata and inherited-metadata as 'editable-metadata'. Also, add unit test for draft metadata-inheritance and publish

- 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

* 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 :)