R10: Add PUT user/:user_name
R1464: Adds holdingbranch (Checkout library) to the checkout fields
R10: Assert there is something in data parameter
R1464 [Follow-up]: Adds holdingbranch (Checkout library) to the checkout fields

 - Use branchname instead of branchcode.
Merge remote-tracking branch 'origin/ft/R1464'
Add documentation for POST /user