Functions for applying Across-track(row-wise) and Along-track(col-wise) corrections to difference maps and source DEM

[ShashankBice]

Hi David,
These 4 functions include:

• Function to compute row/col wise correction fits
• Function to plot dh map before and after applying the fit, with plots of corresponding correction surfaces
• Function to plot the noisy median+smoothed correction fit signal
• Function which wraps the above three, accepts dem_align.py's source DEM (*align.tif), difference map (*align_diff.tif) and filtered difference map (*align_diff_filt.tif).
  I was not able to write the wrapper cli script, can take a stab later next week. Thanks for the great suggestions and guidance !

[dshean]

Sorry I failed to merge this earlier. Going to merge now, and clean up. Not sure we want imview as another top-level dependency if we can avoid it.