Restyle navigation bar to be more in line with Lion.

- The shading is a combination of the scope bar and textured button used in Lion/Mountain Lion.
- Add an inactive state.
- Increase click area of the forward/back buttons while decreasing the image size.
- Switch popup menu cell to NSBackgroundStyleLight, previously the text would go to gray when inactive this prevents that though it does lose the drop shadow.
- Various tweaks to alignment and spacing.