Consistent fiber tracing of centroid and FWHM

[ajmejia]

Implementing a consistent fiber tracing of centroid and FWHM using Gaussian profile fitting per blocks. Main changes are:

• Implementing data interpolation method in TraceMask class
• Implementing coefficients interpolation method in TraceMask class
• Implementing trace_fibers task using Gaussian profile fitting (superseding trace_fiber_fwhm)
• Prototyping fiber tracing procedure and fiberflat creation using standard fiber exposures sequence