Bug 5354: Partial duplication of a subscription

Bug 5354: Partial duplication of a subscription

A new syspref (SubscriptionDuplicateDroppedInput) contains the list of fields to
duplicate when duplicating a subscription. The library will be able to
define that, for example, the internal note should not be duplicated

Test plan:
On the detail subscription page, click Edit > Edit as New (Duplicate):
All the information must be copied from the original subscription.

Fill the syspref SubscriptionDuplicateDroppedInput with a list of fields
you don't want to be duplicated (e.g. location;notes;branchcode).

Repeat the duplicate action. Normally, information for these fields are
not copied.

Signed-off-by: Kristina D.C. Hoeppner <kristina@catalyst.net.nz>