Show StockChanges index

It often occurs in our foodcoop that virtual stock quantities do not match the real ones. In order to investigate the reason, this small addition would be a great help.

See also foodcoop-rostock#48

- [x] Make stock_changes readonly in index view if possible (so that bugs are avoided)
- [x] Create real links to order/delivery/stock_taking
- [x] Update locales
- [x] Move to stockit controller and view directory?