Allow Militia, Caravan, Bandit Boss to be acquirable via upgrade as well as link them to each other

This mod does not require new save and can be add or remove at any time. However, better safe than sorry. So you should always back up your save

Tested on 1.1.4 but it should be very compatible with most version (until it didn't, please try first)
//Update: 1.2 Still Work...

Main Version: Upgradable and Connected (Save Safe)
- Peasant can upgrade to Militia
- Militia can upgrade to Veteran version
- Caravan Troops now upgradable (Armed Trader -> Caravan Guard -> Veteran/Master)
- Bandit Boss unit now acquirable via upgrade
- Militia Archer can upgrade into Armed Trader
- Militia Spearman can upgrade into Generic Merc Troops

Why? Well,...
-> militia are peasant called in to served... you got the point. it should be the part
-> veteran version... obviously
-> Bandit to Boss? Again, make 10x more sense than become noble troops
-> Those who served as militia either stay there (veteran) with limited career part or to sell their skill some where else (merc/caravan)

Not convinced? Want simpler version? fine...

Alternate Version: Upgradable (Save Safe)
- Militia can now upgradable
- Caravan Troops now upgradable
- Bandit Boss unit now acquirable via upgrade

Future Plan:
- Ensure that this continue to work if they change stuff