Update MANIFEST.in from cubicweb 3.26 skeleton

But exclude debian directory since I don't understand why we would
need it in the sdist.

MANIFEST.in

-include setup.py
-include README
-include *.ini
-recursive-include cubicweb_postgis *
+include *.py
+include */*.py
+recursive-include cubicweb_postgis *.py
+recursive-include cubicweb_postgis *.sql
 recursive-include cubicweb_postgis/data *.gif *.png *.ico *.css *.js
 recursive-include cubicweb_postgis/i18n *.po
-recursive-include cubicweb_postgis/schema *.sql
+recursive-include cubicweb_postgis/wdoc *
+recursive-include test/data bootstrap_cubes *.py
+include *.ini
 
+prune cubicweb-postgis.spec
+prune debian