Make the AI use diplomacy features

[SamTheBlow]

For 4.1, I want to add a few different AI personalities when it comes to diplomacy. Here are the tasks.

Game rules

• [x] Default AI personality option (default is the one that does nothing)
• [x] Assign a random AI personality to all players at the start (bool, false by default)

Code architecture

• [x] Create a new class AIPersonality; just like Action, it's an abstract class where each subclass has its own id
• [x] PlayerAI has an AIPersonality; it defaults to what the game rule says
• [x] Do the random personality assignment at start of game if the game rule says to
• [x] When it's the AI's turn, it asks its personality for diplomatic actions

Personality: "Interventionist"

• [x] Tends to be at war with at least one reachable nation
• [x] Tends to declare war on nations that are getting too strong
• [x] Tends to send & accept peace/alliances with weaker nations
• [x] Tends to declare war on the enemies of its allies

Personality: "Isolationist"

• [x] Tends to go to war with the weakest neighboring nation, but only when much stronger than that nation and its nearby allies
• [x] Tends to send & accept peace/alliances with all nations

Personality: "Shy"

• [x] Tends to be at war with one reachable nation who is already at war with another nation
• [x] Tends to not break alliances (unless it has to for previous point)
• [x] Tends to ask for peace, but not alliances
• [x] Tends to accept diplomatic offers

Personality: "Greedy"

• [x] Tends to be at war with at least one reachable nation
• [x] Tends to declare war on weaker reachable nations
• [x] Tends to seek peace with everyone else
• [x] Tends to only accept offers from stronger nations
• [x] Tends to offer alliances with strong nations

Personality: "Emotional"

• [x] Tends to be at war with the enemies of its allies
• [x] Tends to accept alliance offers
• [x] Tends to refuse peace offers
• [x] Tends to offer alliances and declare war at random

Personality: "Erratic"

• [x] Tends to be at war with at least one reachable nation
• [x] Tends to accept or ignore offers at random
• [x] Tends to make offers at random

Personality: "Test AI: accepts everything"

• [x] Accepts all diplomatic offers

Save and load

• [x] Save the AI personality of each player
• [x] Load the AI personality of each player

Networking

• [x] Make sure the RNG is always the same across clients