add target_location_namespace check

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

Added tests for importing a pure XBlock

Fix donwload subs for non youtube videos and non-en language - continue.
Add acceptance tests.
Add detetion of assets on request.
Updated docstring.
Add fixes and acceptance tests.
Fix acceptance tests.
Update docsrtings and cleanup code, resful for language_id.
Specify exception type in POST.
Fix url in upload module.
Improve exception handling.
Remove 'en' and catching in editable_metadata.
Move descriptor.get_context test to lms tests.
Add query parameter to translation dispatch.
Response to format parameter of translatin GET request.
Fix Acceprance test: Metadata Editor.
move handlers to proper scores.
Split video player into smaller files.
Add ugettext and fix typoes.
Add changelog.
Support for downloading non-ascii filenames.
Change event binding.
Add content-language to download requests.
Reractor POST handler to not update self.transcripts.

STUD-1433

LMS-1192

STUD-1359

Currently wiki_slug is set to course number. However, since multiple
courses can have the same number this may lead to clashes. So wiki_slug
will be set to org.course.name. To maintain the active wiki_slugs for
xml courses this cannot be changed in the CourseDescriptor.

LMS-2136

Also fixes STUD-1351

update course info module to save content in new 'items' field + update import/export to handle content field other than 'data' or 'metadata'
STUD-154

STUD-149

STUD-1027

[LMS-179]
[LMS-209]
[LMS-1345]

Add tests

STUD-714

STUD-878

Part of STUD-91

Part of STUD-868

These files seem to have been copied over from old XML courses,
and shouldn't be in our repository.

One test passes already, the other fails.  Fix in next commit.

One test passes already, the other fails.  Fix in next commit.

Pattern for how to do refactoring from locations to locators and from
old style urls to restful ones.

Make tests conform to new import UI

Previously, these tests modified due_date, which failed due to the new
restrictions on writing to Scope.settings from the LMS.

By transparently proxying between the XModuleDescriptor and the XModule,
and between their runtimes, we can make them act as a single class, so
that we can swap in an actual XBlock instead.