Use map_outer_window_stats for rx and matched_filter.

- algorithms/detectors.py:
  (MatchedFilterWrapper): Deleted class
  (WindowedGaussianBackgroundMapper):
  - Moved to spatial.py
  - Now supports slices and non-square windows
- algorithms/spatial.py:
  (map_window):
  - Renamed (was apply_windowed_function)
  - func arg now expects second input (pixel row/col)
  - accepts tuple window arg
  (inner_outer_window_mask_creator): can produce windows with even dimensions.