Prefer numeric_limits from standard library

[SunBlack]

Use std::numeric_limits instead of custom implementation of numeric_limits or numeric_limits without std:: prefix (further preparation for #3235)

--expt-relaxed-constexpr (docu) was necessary, because of:

/media/sf_pcl/gpu/kinfu/src/cuda/utils.hpp(126): error: calling a constexpr __host__ function("epsilon") from a __device__ function("computeRoots3") is not allowed. The experimental flag '--expt-relaxed-constexpr' can be used to allow this.

Was not sure if you want to deprecated custom implementation first, but to switch to std::numeric_limits from pcl::device::numeric_limits is not this complicated ;-).

[SunBlack]

Added some constexpr and reduced scope of variables (last to prevent Cppcheck warnings).