feat(inventory): add inventory total value or selected items' value text

[HoloTheDrunk]

Is your feature request related to a problem? Please describe.
It would be nice to be able to get a rough idea of how much a group of items (or an entire inventory) is worth.

Describe the solution you'd like
Option 1: Entire inventory
Option 2: Implement item selection in inventory and add a Select All button
Both: calculated value in textbox at the top of the inventory.

Additional context
Basic UI idea (entire inventory info):