Paypal express should formally support recurring

Paypal express supports recurring on a technical level - ie, IPNS work and payments get created etc. However, it is disabled in the UI on the assumption it doesn't work (which pre-dates various changes). I think apart from the loss of functionality this actually makes the code less stable.

Here is the proposed sql to put in an upgrade script

UPDATE
civicrm_payment_processor_type pp
LEFT JOIN civicrm_payment_processor p ON p.payment_processor_type_id = pp.id
SET pp.is_recur =1, p.is_recur=1
WHERE pp.name='PayPal_Express'