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:** 
- [x] add empty state for accordion and slider (add new child)
- [x] add inset styling according to screenshot, expect for first level
- [x] show brick header with buttons on rollover
- [x] show save button below main inputs of a brick
- [x] add title + brick type to brick header
- [x] "add element" dropdown is now contained in the header
- [x] all forms are stacked

**Points:** 3pt, needs Design Team input