LP#1777675: Fix code to update Item Status grid

LP#1777675: Fix code to update Item Status grid

Testing revealed that the grid rows use a different data structure, and
the object member names include dots (periods). Thus, bracket notation
is required to access those members.

This commit also makes a few smaller changes:
  - Prevents an error in the Check-in app when a last_copy_inventory
    doesn't exist yet.
  - Removes the "refresh" parameter from the updateInventory() function,
    which is never supplied when called, nor used by the function.
  - Adds some brief code comments.

Signed-off-by: Remington Steed <rjs7@calvin.edu>
Signed-off-by: Dan Wells <dbw2@calvin.edu>
Signed-off-by: Kathy Lussier <klussier@masslnc.org>