Bug 971483 - [System2] Instantiable DevToolsLayer r=alive

https://bugzilla.mozilla.org/show_bug.cgi?id=971483

Renaming this to be DevtoolsView to be more inline with our TTLView class.

Screenshot of JSDoc:

![screen shot 2014-02-12 at 6 09 11 pm](https://f.cloud.github.com/assets/122602/2156113/dedb3de0-9453-11e3-9078-b91861e880ce.png)