Sort collections in media-selection overlay

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- [ ] gather feedback for my changes
- [ ] submit changes to the documentation

__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | yes
| Fixed tickets | none
| BC Breaks     | none
| Doc           | none
You should make sortBy an array.

````
$sortBy = array('foobar' => 'asc');
````

This allows the following in the future:
````
$sortBy = array('foobar' => 'asc', 'barfoo' => 'desc', 'blahblah' => 'desc');
````

It will be a requirement one day.