NPC: Cleaned up debugging logs.

Standarized logs to have different levels.
Show by default only INFO, ERROR log messages.
Dialogues: Standarized function for NPC chat messages.
Removed trader.lua and trader_test.lua which are part of old 'mobs_npc' mod.

init.lua

@@ -23,7 +23,6 @@ else
 end
 mobs.intllib = S
 
--- NPC
 dofile(path .. "/npc.lua")
 dofile(path .. "/spawner.lua")
 dofile(path .. "/relationships.lua")