[FEATURE] use pseudo/seeded RNG on the choice of entity templates

[Aelto]

At the moment the entity templates are picked randomly whenever an entity is spawned by the mod, that means bounties and contracts may not spawn the exact same entity if a player dies and reloads the save.

• generate seed number from encounter's position and maybe other values for extra randomness
• update spawning code to use said seed while picking entity template