Increase the z-index of the media modal, so it appears on top of the ctools modal used by IPE.

Problem/Motivation

I have a bug where the media modal is appearing behind the modal used to edit content on a page. Steps to reproduce:

1. Navigate to any page that uses IPE.
2. Edit the content, ensuring it can be done so with a media enabled WYSIWYG.
3. Open the media modal.
4. Observe it appearing under the IPE modal.

The fix is quite simple, but I'm using a customised version of commons, so I'm not sure if this is a problem with a completely out of the box setup or requires some degree of configuration.

Proposed resolution

Fix the z-index.

Remaining tasks

Patch.

User interface changes

Working modals.

API changes

None.

Data model changes

None.