Menu Bar component

The Menu Bar should be a flexible, highly-customizable, all purpose menu bar. Its origins are in the Icon Bar in Foundation 5, but this component will have more options for icon placement and secondary features like labels.

**Features:**
- [ ] Horizontal and vertical orientation, with breakpoint classes for both
- [ ] Icon positioning (left, top, right, bottom)
- [ ] Spacing options (e.g., left-aligned items, evenly-spaced items)
- [ ] Count labels (i.e., unread message count)

**Component requirements:**
- [ ] Settings variables
- [ ] Layout mixins
- [ ] Style mixin