Rework Avatar journey events

[unLomTrois]

I've made an overhaul only for air nomad arc, we have to add updated arcs for water, earth, and fire too
Each arc should be like 15-20 events, to show the very essence of the journey
Events should describe the locations, the process of learning the elements, reveal the mores of people
So the list of arcs:

• Air Nomad arc (add an option to learn airending after air nomad genocide)
• Water Tribe arc
• Earth Kingdom arc
• Fire Nation arc (with posibilities to learn firebending during HYW)