Merge !506 Persist the language cookie when changing language

The fact that ERP5 does not remember the selected language has been reported as a bug to us.

Instead of using a session cookie, this change make the cookie persists. For one year. This is a bit arbitrary, I copied that behavior from the "remember my username" [cookie](https://lab.nexedi.com/nexedi/erp5/blob/557c20bdf0e/product/ERP5Type/patches/CookieCrumbler.py#L138) that we use to have on the login page.

/reviewed-on !506

product/ERP5/bootstrap/erp5_xhtml_style/SkinTemplateItem/portal_skins/erp5_xhtml_style/Base_doLanguage.py

@@ -37,4 +37,4 @@ else:
   if not select_language:
     select_language = portal.Localizer.get_selected_language()
 
-  portal.Localizer.changeLanguage(select_language)
+  portal.Localizer.changeLanguage(select_language, expires=(DateTime() + 365).toZone('GMT').rfc822())

product/ERP5Type/tests/utils.py

@@ -175,7 +175,7 @@ class DummyLocalizer:
 
   get_languages = get_supported_languages
 
-  def changeLanguage(self, lang):
+  def changeLanguage(self, lang, expires=None):
     self.lang = lang
 
   def translate(self, domain, msgid, lang=None, mapping=None, *args, **kw):