subscriptions - adding suggested_quantity to Pool
subscriptions - suggested_quantity and instance_multiplier

including suggested_quantity and instance_multiplier into the "Available
Subscriptions" section for Systems.

If a subscription has an instance_multiplier > 1, then the  spinner's
step is set to that. The suggested_quantity is set into a spinner when a
user clicks that subscription's checkbox.
Merge pull request #2543 from komidore64/instance-based-sub-spinner

subscriptions - suggested_quantity and instance_multiplier