Glacial - loop over spol and freq to make graphs

Also added options:

glacial_splitting(..., 'phasepole') -  Generate phase velocity / splitting pole figures
glacial_splitting(..., 'splittingplot') - Plot the wavelets for each effective splitting calc
glacial_splitting(..., 'mode', eff_split_mode) - String passed into the mode argument of MS_effective_splitting_N. Note that setting this to 'GaussianWavelet' results in a much longer execution time.

some documentation and cleanup.