2317193 | Port "Add an item to a list" action to D8
Merge pull request #102 from stevepurkiss/port-list-add-item-to-D8-2317193

Issue #2317193 by stevepurkiss: Port "Add an item to a list" action to D8
Fixed test fails after language manager interface changed to returning classed objects.
Fixed test fails for entity integration tests, EntityManager now has one more constructor argument.
Fixed typo in system message action plugin.