Add option (n_extra_bins=3) to cctbx.xfel.merge to include extra rows

[phyy-nx]

Consider the existing table of resolution bins, with the final row being 'all'. Add n_extra_bins past d_min cutoff.

Means that the resolution filter needs to filter out farther resolution.

In postrefinement, or any code that uses the reflections as input, use only d_min filtered refls to compute corrections, but apply corrections to all refls. To do this, use the existing reflection table 'flag' infrastructure.