Check for max offset

[oleg-alexandrov]

The dem_align.py program has the following logic:

dm_total = np.sqrt(dx_total**2 + dy_total**2 + dz_total**2)
       if dm_total > max_offset:
           sys.exit("Total offset exceeded specified max_offset (%0.2f m). Consider increasing -max_offset argument" % max_offset)

However, -max_offset is meant to be the horizontal offset (the vertical one is max_dz). So, there will be a failure above if the produced z offset is large but max horizontal offset is small, which is likely not intended.