Add multiple transcripts editor.

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.
Fix typo.
Add tests for translation DELETE dispatch.
Update acceptance tests.
Add tests for POST dispatch.

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.
Add test for sub_filename.
Move dispatches to suffixes and fix quality.
Support for downloading non-ascii filenames.
Change event binding.
Address comments.
Remove prompts.
Add content-language to download requests.
Remove DELETE dispatch and clear tests.
Reractor POST handler to not update self.transcripts.
Fix tests.
Address comments.