Added a quick check to load_by_label() to see if the FCC or FM mask has
an 'extras' field (if not, it fills it with 'none').
Added a short function that calculates the variance given the CDF values
(cdfX, cdfY). This is a very thin wrapper around Matlab's 'var' function
but it makes code easier to read and write.
Moved combine_cochannel_and_adjacent_channel_exclusions() out of
make_fcc_mask.m and into its own file in the Helpers/ directory. Also
added documentation for the function.