Enhance BrickList UI

Heavy nesting makes this UI hard to use... see demo of an Accordion with AccordionItems with Text.
[Screen Shot 2013-01-11 at 16 25 45](https://f.cloud.github.com/assets/234051/60241/46c02ef0-5c03-11e2-9539-10a5c309fd44.png)

**Todos:** 
- [ ] add empty state for accordion and slider (add new child)
- [ ] add inset styling according to screenshot, expect for first level
- [ ] show buttons on rollover unless it's the Save button
- [ ] no save button for bricks which only contain childs and no content by themselves
- [ ] constrain addable childs (see #47)
- [ ] add title + brick type to brick header
- [ ] "add element" dropdown is now contained in the header
- [ ] if possible, show text editor header on rollover
- [ ] all forms are stacked

**Points:** 3pt, needs Design Team input