[12406] Add new SCRIPT_COMMAND_TERMINATE_SCRIPT (31) command to DBScriptsEngine

This command can be used to terminate the execution of a DB Script, depening if an (alive) npc is nearby

Without data_flogs & COMMAND_ADDITIONAL, further steps of the script be will terminated if the provided npc is not found (alive) in the search radius

With data_flags & COMMAND_ADDITIONAL, further steps of the script will be terminated if the provided npc is found (alive) in the search radius

This can (for example) be used to prevent double spawning of an npc.
But remark that the order of the script steps are time depending, so you must be sure that the terminate command is handled before (lesser delay) the commands that should be skipped

(based on commit [12296] - dcf5dd7)