cms.toolbar.modal.scss hides h2 elements in InlineAdmin fields

This prevents nested inlines from being displayed/edited in frontend-editor

Specific case seen when using django-form-designer, the plugin uses H2 elements to control showing/hiding some of the field elements. The rule is written to hide any h2's under #content, and ends up being too greedy.

This fix updates the cms.toolbar.modal scss to prevent greedy h2 { display:none } capture and only target the top level element, while allowing the nested h2's to be shown for interaction

![inlineadmin_before](https://cloud.githubusercontent.com/assets/486461/3345490/f6c0ec92-f8b8-11e3-8816-b018d32a6fd1.png)
![inlineadmin_after](https://cloud.githubusercontent.com/assets/486461/3345491/f98662f4-f8b8-11e3-9822-db65a682487a.png)