vp9-skinmap. Some adjustments for model=1.
vp9-skinmap. Some adjustments for model=1.

-use larger threshold on y (as in vp8).
-add distance threshold for each cluster
-use larger skin distance threshold for first cluster
-add some early exist checks.

Keep default setting to model=0.

Change-Id: I1044b99ade4bb1f215a860a019a4d84cee2f7715

mbebenita/aom,mwgoldsmith/vpx,mbebenita/aom,GrokImageCompression/aom,mbebenita/aom,mbebenita/aom,mwgoldsmith/vpx,mbebenita/aom,Topopiccione/libvpx,mwgoldsmith/libvpx,smarter/aom,smarter/aom,mbebenita/aom,mbebenita/aom,smarter/aom,GrokImageCompression/aom,GrokImageCompression/aom,webmproject/libvpx,webmproject/libvpx,smarter/aom,Topopiccione/libvpx,luctrudeau/aom,Topopiccione/libvpx,Topopiccione/libvpx,GrokImageCompression/aom,mwgoldsmith/libvpx,ittiamvpx/libvpx-1,mwgoldsmith/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,mbebenita/aom,luctrudeau/aom,GrokImageCompression/aom,luctrudeau/aom,mwgoldsmith/vpx,mwgoldsmith/vpx,mwgoldsmith/vpx,ittiamvpx/libvpx-1,GrokImageCompression/aom,Topopiccione/libvpx,ShiftMediaProject/libvpx,smarter/aom,mwgoldsmith/vpx,luctrudeau/aom,luctrudeau/aom,webmproject/libvpx,smarter/aom,ittiamvpx/libvpx-1,ittiamvpx/libvpx-1,mbebenita/aom,mwgoldsmith/libvpx,ittiamvpx/libvpx-1,webmproject/libvpx,ittiamvpx/libvpx-1,luctrudeau/aom,ShiftMediaProject/libvpx,mwgoldsmith/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,mwgoldsmith/libvpx,Topopiccione/libvpx