multiple files upload to playlist keep initial file order

**Acceptance Criteria:**
* [ ] if multiple files are drag'n'dropped onto a playlist the original file order should also be reflected in the added songs of the playlist

Example:

```
Before Upload:
1. Song 1
2. Song 2

Drag'n'Drop
01 - Song 3.mp3
02 - Song 4.mp3
03 - Song 5.mp3

After Upload:
1. Song 1
2. Song 2
3. Song 3
4. Song 4
5. Song 5
```