Fix translate error when subtitle has tailing space.

See full Changelog -->

Fix popup translation source not show on non-YouTube site.

See full Changelog -->

• Use YouTube official translated subtitle first

• Fix sometimes official translated subtitle language label get error

See full Changelog -->

Now we support www.khanacademy.com.

See full Changelog -->

Now we support business.udemy.com.

See full Changelog -->

Now we support embeded nocookie YouTube videos on any site.

See full Changelog -->

Now we support www.futurelearn.com and online.stanford.edu.

See full Changelog -->

Fix "Translation Source" label missing when load from some youtube videos.

See full Changelog -->

Ignore 'auto-generated' subtitle of youtube if possible because of its bad quanlity.

Open this site when user click "Question" icon on the popup window.

See full Changelog -->

Reconstruct translation requests. Improve translation speed and stability.

See full Changelog -->