Update model pane

This guy adds several panes to the model sidebar ("model", "changed", "_previousAttributes") and takes a lot of gunk out of the properties pane. 

![](http://f.cl.ly/items/020P1A0j1U2Z0Q1F390d/Image%202014-11-21%20at%2010.42.48%20AM.png)

We also clean up after ourselves a bit here and simplify the way we get information about objects. We do this by introducing a new helper called `inspectObject` that does three things:
+ returns the value as JSON
+ serializes it
+ and inspects it
+ checks if the object is empty

e.g.
`inspectObject({a: 2, b: function() {2+2});`
```js
{
  value: {a: 2, b: function() {2+2},
  inspect: "{a: 2, b: function() { ... }}",
  serialize: [
     {
        type: 'number',
        value: '2',
        cid: undefined,
        key: 'a'
     },
    {
        type: 'function',
        value: 'function() { ... }',
        cid: undefined,
        key: 'b'
     },
  ],
  isEmpty: false
}
```