SSO and messages

* removes unused third party package from requirements.txt
* adds KonovaSSOClient as subclass of sso.Client for more control over login, e.g. which user data shall not be updated (found in konoa/sso/sso.py)
* adds Messenger class for communicating with SSO server (found in konova/utils/messenger.py)

konova/urls.py

@@ -16,14 +16,14 @@ Including another URLconf
 import debug_toolbar
 from django.contrib import admin
 from django.urls import path, include
-from simple_sso.sso_client.client import Client
 
 from konova.autocompletes import OrganisationAutocomplete, NonOfficialOrganisationAutocomplete, EcoAccountAutocomplete, \
     InterventionAutocomplete
 from konova.settings import SSO_SERVER, SSO_PUBLIC_KEY, SSO_PRIVATE_KEY, DEBUG
+from konova.sso.sso import KonovaSSOClient
 from konova.views import logout_view, home_view, get_document_view, remove_document_view, remove_deadline_view
 
-sso_client = Client(SSO_SERVER, SSO_PUBLIC_KEY, SSO_PRIVATE_KEY)
+sso_client = KonovaSSOClient(SSO_SERVER, SSO_PUBLIC_KEY, SSO_PRIVATE_KEY)
 urlpatterns = [
     path('admin/', admin.site.urls),
     path('login/', include(sso_client.get_urls())),