Bug 20819: Add check in get_template_and_user to enforce GDPR

Bug 20819: Add check in get_template_and_user to enforce GDPR

If you choose to enforce GDPR policy, a user needs to give consent for
data processing before he does something else in the OPAC while being
logged in.

Test plan:
[1] Set GDPR_Policy to Disabled or Permissive. Usual behavior.
[2] Set to Enforced. Save a refusal on your consents. Notice that
    you are logged out when saving. When you login again, all OPAC
    requests are redirected to your consents tab.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Séverine QUEUNE <severine.queune@bulac.fr>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>