Use libtopotoolbox implementations in `FLOWobj.createAuxiliaryTopo`

[wkearn]

A good place to start with libtopotoolbox is in toolbox/@FLOWobj/private/createAuxiliaryTopo. We can do most but not all of the steps in that function using libtopotoolbox. Each of the following libtopotoolbox functions need a MEX wrapper and then should be incorporated into the corresponding function of topotoolbox3:

• Implement fillsinks MEX #19. Wraps our implementation of imreconstruct. Does not handle known internal sinks.
• Implement identifyflats MEX #20. Similar to identifyflats but has a different return value that requires splitting into the desired outputs.
• Implement gwdt_computecosts MEX #21. This function implements this part of createAuxiliaryTopo

        CC = bwconncomp(I);
        tweight = 1;
        for r = 1:CC.NumObjects
            maxdepth = max(D(CC.PixelIdxList{r}));
            D(CC.PixelIdxList{r}) = (maxdepth - D(CC.PixelIdxList{r})).^tweight + CarveMinVal;
            %                             D(CC.PixelIdxList{r}) = maxdepth - D(CC.PixelIdxList{r});
            %                             D(CC.PixelIdxList{r}) = (D(CC.PixelIdxList{r})./maxdepth + CarveMinVal).^tweight;
        end
        clear CC

• Implement gwdt MEX #22. Similar to graydist, but with a different interface