Wrong item removed from initialPreviewConfig after rearrange and delete

[koxu1996]

Simple reproduce:

1. Go to: http://plugins.krajee.com/file-preview-management-demo#preview-data
2. Switch Lighthouse.jpg with Desert.jpg
3. Remove desert image
4. See initialPreviewConfig by entering this in web console: JSON.stringify($('#input-pd').data('fileinput').initialPreviewConfig)
5. Now you can see that desert image still persist and lighthouse is removed!

What cause this:
Unset function use index from html data-fileindex, but this is constant and unchanged after sorting.

Solution:
Update data-fileindex after rearrange

[koxu1996]

@kartik-v I completly edited issue, please take a look.