MVE: App scene2pset updated
Merge pull request #40 from Waldteufel/srgb2lin

DMRECON: precompute srgb2lin mapping
DMRECON: Small style change
DMRECON: share image pyramids between threads

Threads reconstructing views from the same scene simultaneously can
share some of their image pyramids when they both use the same
neighboring view.
DMRECON: refactor ImgPyramidCache access

Now, ImgPyramidCache (instead of SingleView) creates the pyramid when
it's not available. Also use static methods to access the cache instead
of a global variable and protect it with a single mutex only.
DMRECON: implement cache cleanup

Use RefPtr for image pyramids, implement a cleanup function for the
image pyramid cache.
DMRECON: use more const'ness