Select a group of enemy when entering a combat depending on map position

[Turtyo]

Description

Choose an enemy group when entering a new fight, depending on a given distribution of enemy groups

Related issue(s)

Closes #128

List of changes

• Add a function to choose an enemy group based on player position in the map
• Add an EnemyGroup which holds a list of enemies and their position in the scene (this is still not great, because there is no way to check for enemy position in the scene apart from launching the game, open to suggestion on how to handle positions)
• Add a background and a few enemies / enemy groups
• Save data if needed

Tests

None yet, an idea for a test could be to launch the function to choose an enemy a few time and compare to an expected output

Additional notes

The enemies are a bit strong now, you can use the instantWinDeck (at "res://Cards/CardSets/InstantWinDeck.tres") and use it by modifying the _ready of the CardManager (by switching out the default deck).

An idea regarding this deck switching, I found out you can use a tscn as an autoloaded singleton (which I did here). So we could make the default deck an @export and autoload a tscn file, so we could change the deck from the inspector to test, instead of having to change it in the code.