Object Inspector Improvements

- [x] Pre-calculate already cached computed properties
- [x] Keep properties up to date when in the inspector
- [x] Restore possibility to send values to the console
- [x] Ability to modify properties directly from the inspector
- [x] Make the object inspector overlay / contract on small screens
- [x] Tests for all of the above



### Sending values to the console:

Clicking on the envelope on the right will send the value to the console and set it to `window.$E`

![ember_extension_send_console](https://f.cloud.github.com/assets/1061742/868299/f4b180a4-f78f-11e2-9185-2b93d16263e6.jpg)

### Two way binding

Properties in the inspector are now bound to the application's values.

Changing a value in the application will update the value in the object inspector.  Values can also be modified from within the inspector by clicking on the value.

Clicking on a value in the object inspector:

- If the value is an ember object, it will dig into that object for inspection.
- If the value is a computed property that is not yet computed (the value would be `<computed>`), then that value will be calculated.
- If the value is a string, bool, number, or json object, you will enter into edit mode where you can edit that value.  The value in the text field will be evaled, so a string would be `"my string"`.  Exception on eval will default to a string, so typing `Hello` in the text field is equivalent to typing `"Hello"`.

![ember_extension_2_way_binding](https://f.cloud.github.com/assets/1061742/868307/57d34d4c-f791-11e2-92e4-fd0a0cc7f522.jpg)

### Expand / Minimize Object Inspector

The object inspector will start as minimized to give room for the main screen.  It can be expanded in two ways:

 - The inspector expands automatically when an object is sent for inspection
 - Clicking on the "expand" button at the right of the extension

When expanded, the inspector will behave in 2 different ways depending on the screen width.  For screens <= 1500px, the object inspector will overlay over the main outlet (in an absolute position).  For screens greater than 1500px wide, the inspector will push the main outlet to fit next to it.

The inspector can be minimized at any time.

Screenshots below for a screen with width < 1500px

Minimized:
![ember_extension_minimized](https://f.cloud.github.com/assets/1061742/868359/484b0df2-f795-11e2-9119-a7cd5f07ebb8.jpg)


Expanded:
![ember_extension_expanded](https://f.cloud.github.com/assets/1061742/868360/4b83efe8-f795-11e2-971c-cce0c14b7dc3.jpg)