Add clip_geom, buffer and extent under auto_publish conf

[sharkAndshark]

Partly fix #872

[nyurik]

I am not sure, but it might be better to actually change buffer and clip_geom here to None to indicate that we don't have them yet, and keep them unset until much later as part of the instantiate_tables somewhere around db_inf.srid = srid; line.

[sharkAndshark]

@nyurik I was thinking of this also,how about here:

...
db_inf.srid = srid;
update_id_column(&id2, &mut db_inf, auto_tables);
impose_clip_geom(&mut db_inf, auto_tables);
impose_buffer(&mut db_inf, auto_tables);
...

[nyurik]

sure, just maybe it will make sense to rename the update_id_column to update_auto_fields and do all these steps inside one function

[sharkAndshark]

Hi @nyurik Have a good day! :)
It's still a draft, but could you help me a code review in case of any big misunderstanding?

[nyurik]

I made a few fixes in sharkAndshark#52

Once merged, should be good to go

[nyurik]

Looks good, needs docs too

[nyurik]

thanks!