Rebranding "install" as "download", on the central server.

Makes much more sense--you're not installing, you're downloading a package for installation.

@wangguan59 Could you take a look?  Need a little help with indicating that downloads work for installation AND upgrades.

![screen shot 2013-11-21 at 9 01 19 am](https://f.cloud.github.com/assets/4072455/1593634/9453e036-52ce-11e3-9799-1853ee6dac96.png)