save seed bitmap menu

This menu lets you create a seed bitmap, in which each object from the original image is represented by a single black pixel, located at each
object's centroid. Such a bitmap can be used in the Path-to-target menu to evaluate the uniformity of object dispersal. The procedure is as follows:
- You enter the name you want for the seed bitmap in the Bitmap file menu field.
- If you want the bitmap to be created in run-length encoded format (generally a good idea)
set the Run-length encode? toggle to Yes.
- Click on CREATE SEED BITMAP FILE.