stock_transfer model to group stock_movements
transfer can receive inventory from vendor with a reference number
use stock_transfer to move stock between locations
optional reference number for stock transfers
initial admin page for bulk transfer and stock receiving
form to bulk transfer multiple variants between locations
remove button for varaints in bulk transfer
remove spec for stock location specific transfer
accumulate variant quantities allowing the same variant to be added multiple times to bulk transfer
button link to bulk transfer
Fix bulk transfer form styles

Conflicts:
	backend/app/views/spree/admin/bulk_transfer/index.html.erb
Fix stock transfer form

Conflicts:
	backend/app/views/spree/admin/stock_locations/index.html.erb
toggle visiblity:hidden to hide source location if receiving stock from vender
use name and sku for bulk transfers
paginate stock_movements
display shipment or stock_transfer numbers on stock_movement page
Restyle bulk transfer form to make adding variants more usable.

Fixes #2936
add variant details to stock_items api
fetch stock items when stock location changes
refactor bulk_transfer javascript into classes