UI: options dialog: remove labels, make collapsible groupboxes

Mainly two things:
* since the page titles are already written on the left panel, the labels on top were redundant, so I removed them
* I made the group boxes collapsible so you can collapse some settings you don't change quite often

![image](https://f.cloud.github.com/assets/127259/1920584/75d62a58-7dec-11e3-9bda-661b3ecef247.png)