Hi, I wanted to use a repeater-type setting on a page and this wasn't possible yet.

• Added repeater type to the post editor sidebar.
• Indented the repeater items by 20px to distinguish them from top-level settings and to make space for the 'move' handle (otherwise clipped off on the post editor sidebar due to its overflow:hidden).
• Fixed the repeater item style to make the labels consistent with those of the other settings, both in theme settings and post/page settings.
• Fixed the offset of the 'move' and 'ui' elements for hideLabels: false.

I've tested both the post settings and theme settings as much as I could, but this is my first PR to this project. Happy to make any changes.