Adds capability to handle rectangular detectors

Many fixes, discovered in the course of trying to implement a rectangular detector for Ulrich's Photonic Science VHR 11 CCD.  A few other bugs were discovered along the way.  

The detector package is due for a complete refactor; for now, the number of rows, number of columns, and pixel size (assumes square pixels) are specified at the top of the module.  The existing DetctorGeomGE and ReadGE classes will provide the template for the new classes…  stay tuned.