Option for removing already selected values in ChainedForeignKey field

[bsledev]

I would like to have an option for filtering out allready selected values for avoiding duplicate entries.
For example in the test_app you can add a continent with multiple locations (inline) with the first select for country.

Actual behavior

It is possible to add an endless amount of entries with the same country.

Expected behavior

The possibility to only allow the selection of one country once in one continent item.