Improve inventory counting/adjustment

* Add a new column, 'counted_quantity' for indicating the manually counted
  quantity. The 'actual_quantity' will be used for actual quantity that should
  be registered on Stoq after the inventory adjustment.
* Lots of improvements to adjustment editor
  * Use fields on inventory item adjustment editor
  * Add more columns to show more information on inventory adjustment editor
  * Instead of removing the adjusted items from the list, show the
    'is_adjusted' flag on a column
  * Make CFOP optional, although reason is still mandatory

Change-Id: Icf3c7497774487ecad30792086d15a4c809aabcc