Annotations can not be created outside the image boundaries.

[cudmore]

No annotations can be created outside the image boundaries.

This includes

• Spines
• ROIs (spine, segment, and background)
• Segments

For Spines and their ROIs, addSpine() should return None if the given (x,y) or the constructed ROI is outside image.

Same for segments.

This is necessary because we are doing intensity analysis on underlying image and it would be wrong as outside the image, there is no intensity.