factory: get rid of getSubscriptionBundle call

Instead, always fetch all SubscriptionBundle at once
(via getSubscriptionBundlesForAccount). This should speed
up refreshes for accounts with a lot of bundles.

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
factory: optimize BusinessInvoiceFactory

Save one call to the database when computing invoice items.

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>