Facelift for Unique Symbols

A redo of the UI for all unique symbols. Main points:

* Organize elements in a grid
* Fix elements' column widths for consistency
* Get rid of JNumericSpinner (old SIF, replaced by JSpinner)

See #471.

#### Before
![old](https://f.cloud.github.com/assets/2470768/753745/06f08936-e575-11e2-8d9f-94de2b97d7b5.png)

#### After
![new](https://f.cloud.github.com/assets/2470768/753742/01052ae0-e575-11e2-8061-af30bc0d0829.png)