Better import

tracim/views/core_api/workspace_controller.py

 from tracim.models.data import ActionDescription
 from tracim.models.context_models import UserRoleWorkspaceInContext
 from tracim.models.context_models import ContentInContext
-from tracim.exceptions import EmptyLabelNotAllowed, ContentNotFound
+from tracim.exceptions import EmptyLabelNotAllowed
+from tracim.exceptions import ContentNotFoundFound
 from tracim.exceptions import WorkspacesDoNotMatch
 from tracim.exceptions import ParentNotFound
 from tracim.views.controllers import Controller