Added a GlobPathStack Resolver

A new resolver that has a slightly higher priority than PathStack and intercepts paths that look like globs.

Among hopefully other advantages, this will allow configuring collections as follows:

```php
array(
    'collections' => array(
        'js/ember-app.js' => array(
            'js/app.js',
            'js/authenticator.js', // individual files, resolved by PathStack
            'js/router.js',
            'js/routes/*', // glob paths, resolved by GlobPathStack
            'js/transformations/*',
            'js/models/*', // this saves us lazy people a lot of work
            'js/components/*',
            'js/controllers/*',
        ),
    ),
);
```

And when order is not so important:
```php
array(
    'collections' => array(
        'js/handlebars.compiled.js' => array( 'templates/**/*' )
    ),
);
```

#### Some Notes

All files in the glob must have the same MimeType as the first file (creating a MimeResolver for this might be a good idea in the future?). This is enforced anyway if within a collection so it shouldn't be a problem because the collection will throw an exception. But outside a collection (e.g. if using a simple Map resolver) GlobPathStack will probably just concatenate all files as usual and silently serve the result with the MimeType of the first file.

Another important note is that it doesn't seem to work within the MapResolver for example (or at least my test didn't work). More generally speaking: I didn't spend any time trying to get it to work outside the CollectionResolver.
`!empty()` is probably better here.