[FIX] Compile for unreal engine 4

Change the plugin version to 15

Bug fixes

Fix changelog

Update CHANGELOG

Advance version to 12.3

Merge branch '25-server-crash-fix' into '4.24'

Fix Crash when running editor as dedicated server

See merge request NotYetGames/DlgSystem!5

Update CHANGELOG

Update CHANGELOG (add date of release for v12)

Hot fix for a crash introduced in v11