Add UNKNOWN functional status to BE

[jyeshe]

Hi, would it possible to add please this functional status? It's required from one of our clients (an OpenFn client)
I have opened the pair PR on openlmis-cce: OpenLMIS/openlmis-cce-ui#9

Change

Adds new functional status to allow saving CCE Inventory with UNKNOWN status.

Build

$ docker-compose run cce
# gradle clean; gradle build
# exit
$ docker build . --tag openlmis-fork/cce

To use it change on the docker-compose.yaml of the openlmis-ref-distro to use the openlmis-fork/cce

Additional notes

This branch was created from the openlmis-cce v1.3.3 tag. The version is the one used by the openlmis-ref-distro v3.17.0