Sandbox button

This pull request enables a "Sandbox Button" under the "Tools" menu, to be used after importing with updraft. It only works under domains containing the word "sandbox", like "sandbox4.something.com".

This is how it looks like:

![captura de pantalla de 2014-12-03 18 01 28](https://cloud.githubusercontent.com/assets/452823/5284704/6c2a83dc-7b16-11e4-8472-ed9c284c3cca.png)