Facelift for Interval classifications

A redo of the UI for all interval classifications. Main points:

* Organize elements into different categories
* Make palette combo box take up less space and put source in tooltips
* Rename "Unit of measure - stroke width" --> "Border width unit"
* Rename "Unit of measure - size" --> "Size unit"
* Rename "Enable stroke" --> "Enable border"

#### Before
![old](https://f.cloud.github.com/assets/2470768/731568/7eb78c76-e26e-11e2-9515-295927235fa0.png)

#### After

**Edit**: Update screenshot

![new](https://f.cloud.github.com/assets/2470768/743309/318a8926-e3e5-11e2-91ff-0076be90657e.png)