Add progress bar for language pack updates

Solves issue #1141 by adding a progress bar during language pack download.  

This includes progress for each stage (download, unpack, etc), as well as progress within the download stage indicating how much of the language pack has been downloaded.

In order to accomplish this, I refactored the video download code, so that it could be used for both.

![screen shot 2013-12-16 at 8 13 22 pm](https://f.cloud.github.com/assets/4072455/1757904/c0028892-6686-11e3-96f6-96314ecb96db.png)
![screen shot 2013-12-16 at 8 13 27 pm](https://f.cloud.github.com/assets/4072455/1757905/c005e640-6686-11e3-9bdc-402ed9e42ac1.png)