Inventory move tool should use stdin

[trickeydan]

When moving many items, it is useful for the inv-mv command to accept part codes on stdin separated by newlines so that we can scan codes in.

[PeterJCLaw]

Note: the current workarounds for this are:

• For incremental moves (part codes checked and items moved as they're input, but slower overall as the inventory is reloaded each time)

  $ xargs -l sr inv-mv

• For bulk moves (part codes checked and items moved all in one go at the end, but possibly faster overall as the inventory is only loaded once; this approach also makes no changes at all if any of the part codes error)

  $ xargs sr inv-mv

The ideal solution would likely have inv-mv able to let the user decide the approach when a part-code is wrong (i.e: what to do with the other part codes) and wouldn't involve loading the inventory more than once.