Add model profile and extraction from NEMO ANHA12 product

[douglatornell]

Birgit uses 5-day-average NEMO output files from Paul Myers' ANHA12 configuration. The file names are patterned like
ANHA12-EXH006_5d_gridT_y2002m01d05.nc
with the day incrementing by 5.

So, core.extract.calc_ds_paths() needs to have a way of stepping through the date range 5 days at a time.

This is somewhat related to issue #32 and requirements identified in pull request #40.

[douglatornell]

Birgit's work is done. So, this feature no longer has a use-case in the group.