Manage gift cards

Following https://discuss.tryton.org/t/manage-gift-cards/2612

assigned to @ced

added type::feature + 1 deleted label

review315331002 updated at https://codereview.tryton.org/315331002/#ps291521002

review315331002 updated at https://codereview.tryton.org/315331002/#ps297651002

review315331002 updated at https://codereview.tryton.org/315331002/#ps303441002

Ready for testing.

added 1 deleted label and removed 1 deleted label

review315331002 updated at https://codereview.tryton.org/315331002/#ps325201002

review315331002 updated at https://codereview.tryton.org/315331002/#ps323331002

review315331002 updated at https://codereview.tryton.org/315331002/#ps323341002

review315331002 updated at https://codereview.tryton.org/315331002/#ps293801002

review315331002 updated at https://codereview.tryton.org/315331002/#ps329591003

review315331002 updated at https://codereview.tryton.org/315331002/#ps340071002

review315331002 updated at https://codereview.tryton.org/315331002/#ps343771003

review315331002 updated at https://codereview.tryton.org/315331002/#ps361511002

New changeset 064d2dcd6235 by Cédric Krier in branch 'default':
Add sale_gift_card module
https://hg.tryton.org/modules/product/rev/064d2dcd6235

added 1 deleted label and removed 1 deleted label

closed

New changeset e5acdc50c2e8 by Cédric Krier in branch 'default':
Add sale_gift_card module
https://hg.tryton.org/modules/sale_gift_card/rev/e5acdc50c2e8

New changeset 7e63420b8f15 by Cédric Krier in branch 'default':
Add sale_gift_card module
https://hg.tryton.org/readthedocs/rev/7e63420b8f15