Fixed column block test

* Fixed setting color to index instead of desired value
* Fixed testing entire column block. Column blocks are overlapped by one pixel intentionally so that we can correct `np.argmax(img) == 0` errors.
Fixed tests

* Fixed usage of `np.ma.MaskedArray`. Masked arrays are not very useful in numpy, so 0 is used to indicate a non-edge index.
* Fixed fragile testing of edge finding above/below the threshold. With a high threshold, it's possible to find an edge in the middle of the test subject's face, which then causes tests to fail. Fixed by filtering parts of the edge with a 0 index.
Cleaned up debug img save, print statements
Better defaults