testutils: force localisation in web tests
testutils: force localisation in web tests

* In testutils, when preparing the Firefox browser instance, use
  a profile where the accept_language is set to 'en', so that the
  default localisation of Invenio is English.

* After login, check if the language is correct and otherwise redirect
  the user to the correct language.

inveniosoftware/invenio,tiborsimko/invenio,inveniosoftware/invenio,tiborsimko/invenio