STUD-1306

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.

Fixed grading tests

Embedded discussion component defaults to "Discussion"
Blank HTML page defaults to "Text"
Video component defaults to "Video"

These default names show up in tooltips.

This standardizes the XModule field default values to be the same as the
values that are presented by studio when a component is added to a
course.

TODO: This breaks the 1.5x and .75x speeds. I'm still looking into
why.

TODO: VideoDescriptor inherits from RawDescriptor in order to
use the from_xml and export_to_xml methods. This seems really ugly,
though; I'd rather find a better way to do this.