Sfm fixes

[PhilLab]

Fixes compilation error with MSVC < 2015 and enables refinement of intrinsics

[sovrasov]

👍

[PhilLab]

Mentioning @edgarriba , just in case the other way around was intended (disabling intrinsic refinement everywhere instead of enabling it everywhere)

[LaurentBerger]

@PhilLab ( and @edgarriba) with your PR I have got some problem to run example given in doc (Sagrada Familia) because of this line
Without optimisation example is able to reconstruct scene but unable to reconstruction when parameters are refined.

I understand that your PR is usefull but I think a function must be added to sfm classe which can process parameters given in libmv_ReconstructionOptions libmv_CameraIntrinsicsOptions
My questions are : can you reproduce problem with example? What do you think about a new method?

Thanks for your answer