Auto install bundle

Automatically install extensions "bundled" with installer on startup.

**Issues**:
* Should appReady in ExtensionManger be used instead?
* Terminology: folder name and location

cc @dangoor @peterflynn 

Code Style: this would look a bit better like so:

```js
var validatePromise,
    srcPath  = FileUtils.getNativeBracketsDirectoryPath(),
    dirPath  = srcPath.substr(0, srcPath.lastIndexOf("/")) + "/bundles/",
    deferred = new $.Deferred(),
    bundles     = [],
    updateZips  = [],
    installZips = [];
```