I have come quite far with the viewer the last few days. The screenshot below show the latest version:
Click on the image for a bigger version.
The viewer will now display a jetmap instead of a blue colour, which I think is nice. You can control the upper and lower thresholds by typing them into the textfields above the viewer. The tool is now also printing the MNI-coordinates and the value of the voxel.
There are still a few things to do, but I should be able to upload the tool to App Store really soon!!!