[pkg] ensure scripts and test files are included in sdist python package

MANIFEST.in

 include *.py
 include views/*.py
+include scripts/*
+include cubicweb-email.spec
 recursive-include data external_resources *.gif
 recursive-include i18n *.pot *.po
 recursive-include migration *.py
 recursive-include views *.py
 recursive-include doc *.txt *.html
-
+exclude test/data/database/*