UI: remove top labels, use collapsible groupboxes, and other small improvements

I update these 3 dialogs: main options, raster properties and vector properties doing 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

Main options:
![image](https://f.cloud.github.com/assets/127259/1920584/75d62a58-7dec-11e3-9bda-661b3ecef247.png)

Raster layers:
![image](https://f.cloud.github.com/assets/127259/1921050/2bf92e14-7df4-11e3-87d7-982b506ff4ad.png)

Vector layers:
![image](https://f.cloud.github.com/assets/127259/1921027/e80f33ba-7df3-11e3-9a4b-9172b3fd0f3e.png)


For vector layers, I also (see previous image):
* moved the field buttons into their corresponding group box
* put the "attribute editor layout" and "python init function" on the same line to gain some room