[mve export] bug fix to enable UID
[mve export] bug fix to enable UID

- Fix remapping view ID to index for camera and for 3D points
visibility.
- Don't export unreconstructed views: as we are doing a remapping from
viewId to viewIndex, it doesnt make sense to keep unreconstructed views.

Note: MVE supports unreconstructed views but not random IDs (as we can
do in openMVG with UID). MVE checks that "view_id < views.size()":
https://github.com/simonfuhrmann/mve/blob/8464613b6608a4fc7faee467397aba59fd0214f4/apps/dmrecon/dmrecon.cc#L289

poparteu/openMVG,poparteu/openMVG,poparteu/openMVG,poparteu/openMVG