Allow clients to retrieve available items for a given location

[jmiranda]

See discussion https://community.openboxes.com/t/api-request-for-zones/954/3 for details and workaround.

Requirements

• Should create a new nested resource for Available Items (or just Inventory Items) under Location API that returns Product Availability records for a given location.
• Should include the following data
  • Location
  • Zone
  • Bin Location
  • Product name
  • Product code
  • Lot number
  • Expiration date
  • Quantity on Hand
  • Quantity Available