#10 Designate ROIs by coordinate & radius

[Victorovitch3]

1) This will avoid having to have image files.
2) Also, we need to allow non-integer coordinates in ROI creation, for more exact specification of ROIs!
3) We'll need a way to distinguish image file ROIs and coord/radius ROIs
4) Implement some sort of thresholding such that we don't need to threshold ROIs manually!