[texturing] improve RAM consumption
[texturing] improve RAM consumption

* don't store pixel mapping between all cams pixels to pixels in final texture, resolve them on the fly while iterating over cameras (cost a little more CPU time, but save a lot of RAM)
* clean up unused method based on barycentric coords
poparteu/openMVG,poparteu/openMVG,poparteu/openMVG,poparteu/openMVG