Add button to force process in purchase_requisition

When approving a purchase_requisition, queue is used to process requisition. But in case of queue is not working we need a button to force process.

assigned to @maxx

added purchasing + 1 deleted label

added 1 deleted label and removed 1 deleted label

New review274941016 at https://codereview.tryton.org/274941016/#ps301071011

added type::feature label

New changeset 9d266c755dd3 by Maxime Richez in branch 'default':
Add button to process requisition
https://hg.tryton.org/modules/purchase_requisition/rev/9d266c755dd3

added 1 deleted label and removed 1 deleted label

closed

New changeset d31468bb027f by Cédric Krier in branch 'default':
Add button to process requisition
https://hg.tryton.org/tryton-env/rev/d31468bb027f