CMS-1028 Content Manager Edit Form - Fix array handling for FormItemSets

In current implementation there are several problems that need to be adressed, particularly related to array handling

Before starting this task, CMS-1027 should be fixed first.
Basically, this implementation is similar, but now applies to FormItemSets and has a few differences.

Important: FormItemSets are not intended to be pluggable (like inputs) at least for now. So array implementation may be handled by the form-renderer directly.

* When minoccur=0 it must be possible to delete all formItemSets, however the "Add NNN" button must never go away!
* When maxoccur is reached, the "Add NNN" button must be disabled (similar to textLines)
* When minoccur>0 the number of formItemSets matching minOccur shall not be possible to remove (no x)
* The collapse all button is repeated between each formItemSet, it should only be listed after the final item. Also, the link is not working (implement according to attached design)