Created a new RectangleCreator class.  In the process of stripping out any unneeded functionality.
Rectangle draws on the image.  Signal/slot hook-ups implemented.
Rectangle now transmits the correct coordinates, width/height measurements via signals and slots.
Created a BackgroundCalculation class to calculate the mean of the voxel values in the rectangle area.  If the user adds an image, a red rectangle automatically appears.  The user can then position the rectangle wherever on the image, and then press the Update button.  The calculations are done, and the mean is stored in the data field next to the Update button.
Removed unnecessary variables