creates _check_log_gaussian_params
creates _check_log_gaussian_params

this creates a helper function that does the checking of the parameter
values and trainability based on orientation_type, eccentricity_type,
and vary_amplitude

also small change, adding "drop_voxels_near_border" to
construct_df_filter docstring

billbrod/spatial-frequency-preferences,billbrod/spatial-frequency-preferences,billbrod/spatial-frequency-preferences