Language pack download UI

Addresses #853. This introduces a working download language pack UI that eventually calls to languagepackdownload command. 

Affected by #1069, but it still downloads anyway and it shows the languages that are installed, dynamically.

![screenshot 2013-11-22 at 09 51 17](https://f.cloud.github.com/assets/191955/1602824/bb6d2c10-539e-11e3-8b8a-7c98460ae185.png)