sparse_disp: clean up im_subset class, add new methods
sparse_disp: clean up im_subset class, add new methods

DougFirErickson/StereoPipeline,oleg-alexandrov/StereoPipeline,ScottMcMichael/StereoPipeline,njwilson23/StereoPipeline,njwilson23/StereoPipeline,oleg-alexandrov/StereoPipeline,DougFirErickson/StereoPipeline,aaronknister/StereoPipeline,DougFirErickson/StereoPipeline,DougFirErickson/StereoPipeline,ScottMcMichael/StereoPipeline,oleg-alexandrov/StereoPipeline,njwilson23/StereoPipeline,NeoGeographyToolkit/StereoPipeline,oleg-alexandrov/StereoPipeline,aaronknister/StereoPipeline,oleg-alexandrov/StereoPipeline,njwilson23/StereoPipeline,NeoGeographyToolkit/StereoPipeline,njwilson23/StereoPipeline,NeoGeographyToolkit/StereoPipeline,aaronknister/StereoPipeline,njwilson23/StereoPipeline,oleg-alexandrov/StereoPipeline,NeoGeographyToolkit/StereoPipeline,ScottMcMichael/StereoPipeline,ScottMcMichael/StereoPipeline,DougFirErickson/StereoPipeline,ScottMcMichael/StereoPipeline,NeoGeographyToolkit/StereoPipeline,DougFirErickson/StereoPipeline,aaronknister/StereoPipeline,ScottMcMichael/StereoPipeline,NeoGeographyToolkit/StereoPipeline,aaronknister/StereoPipeline