Fix for bug BLD-277

"There is a white panel over a non-youtube video."
When the captions file is not specified, we simply do not render the captions panel.
Added Jasmine test for bug fix. Updated comments.
Fixing code as per suggestions on PR 771.
Remove caption panel when anything bad happens.

Now the captions panel will be shown with captions only after successful
retrieval of captions.
Applying code changes as suggested by Anton.

Fixed 2 failing Jasmine tests. Removed unnecessary console.log() call.
Initializing of variables in a single var statement.
Using native Jasmine-jQuery method to check for hidden el.
Merge pull request #771 from edx/valera/fix_empty_captions_panel_no_captions

Valera/fix empty captions panel no captions