celery: fix email reporting

* Fix an issue preventing error emails from being sent.

Signed-off-by: Lars Holm Nielsen <lars.holm.nielsen@cern.ch>
WebAccess: improve login performance

* Adds argument batch mode in acc_authorize_action to lower number of
  database queries when testing many arguments against the same action
  and user.

* Improves login performance by using the acc_authorize_action
  argument batch mode to calculate list of permitted collections for
  a user.
WebSession: fix permission issue for guest user

* Fixes a permission issue where a guest user did not have a list of
  permitted restricted collections calculated, causing issue with
  e.g. facets when viewing restricted collections (e.g. restricted to
  role anyuser).
web_api_key: add option to disable signing

* Adds option to disable need for signing an API request.