Minor ui fixes in GWTConfigPanelVisual

* added mnemonics
* aligned naming scheme of labels
* make link compatible to darkthemes (>=NB7.4, still works in NB7.3, hardcoded color was removed)

![2013-10-24_23h17_44](https://f.cloud.github.com/assets/1857095/1403794/4271cad4-3cf9-11e3-844b-e7aa8e83fb84.png)