Admin Orders-shipments

## Admin side implementation for Unifaun integration

### How it looks:

#### Order-details page
![order-details](http://i.imgur.com/trEuZLc.png)

#### Order-shipments page
![order-shipments](http://i.imgur.com/3kVPCIh.png)

#### Order-shipment-edit page
![order-shipment-edit](http://i.imgur.com/TjyoW50.png)

---

### Not implemented in this:
The `Post to Unifaun` and `Get status from Unifaun` buttons functionality as they depends on the backend xml-integration .

### Test coverage right now:
97 / 102 LOC (95.1%)

### Commit message
- Adds a 'Shipments' link to the order-details page in the sidebar tab
- Introduces an /admin/orders/:order_id/shipments page, where all shipments associated with the order are listed
- Introduces an /admin/order/:order_id/shipments/:id/edit page, for details of a particular shipment
- The order-shipment-edit page contains the buttons for 'Post to Unifaun' and 'Get status from Unifaun'
- The buttons are not functional right now.