New administrative interface

Addresses at least: #193 #364 #974 #689 

Sending this PR now, even though it's not done, so others will be aware of where I'm at, and where I'm heading.

In building documentation for administration of KA Lite, I realized that our admin interface doesn't have overall coherence.  
* There are few entry points for some basic functions (e.g. creating facilities, groups, installing language packs)
* Related functions have very different UI paths (e.g. adding users vs. editing/moving users across groups).
* Terms can be relatively opaque and are not defined.
* No place for access to help / documentation.

I'm redesigning the admin interface with 4 basic actions in mind:
1. **Overview**: A high-level overview of both current status of user data, and current status of syncing
2. **Users**: User management--teachers and students separately--adding, updating, moving, etc.
3. **Videos** (in the future, *Content*): downloading or deleting content.
4. **Languages** (in the future, *Setup*): updating the server setup / configuration, currently by installing language packs.

I believe from this interface, admins will have clear entry points into each function they will want to do, and the user's manual will be much more straightforward.

Here are a few screenshots of where I'm at so far!
![screen shot 2013-12-18 at 10 27 44 pm](https://f.cloud.github.com/assets/4072455/1782090/b59f5960-68a3-11e3-8fd4-8badd8bd812c.png)
![screen shot 2013-12-19 at 2 00 31 pm](https://f.cloud.github.com/assets/4072455/1782145/6101d1a6-68a5-11e3-906d-1de9808cd635.png)
![screen shot 2013-12-19 at 1 57 23 pm](https://f.cloud.github.com/assets/4072455/1782147/625b1e54-68a5-11e3-9c42-2a6fa6ba2224.png)
![screen shot 2013-12-19 at 2 00 52 pm](https://f.cloud.github.com/assets/4072455/1782150/6eb0979c-68a5-11e3-91ec-6759e418ecf8.png)
![screen shot 2013-12-19 at 2 01 01 pm](https://f.cloud.github.com/assets/4072455/1782151/714786a0-68a5-11e3-8a03-64c910a059fb.png)
![screen shot 2013-12-19 at 2 01 09 pm](https://f.cloud.github.com/assets/4072455/1782152/7377a18a-68a5-11e3-958e-7781ca366ced.png)

All are welcomed to comment!  @wangguan59 @rtibbles I know you've dealt with these things before, and hope you might have time for feedback in the next 16 hours--the timeline for rolling something out in Gitwe.