Cascade delete mini game ranking entries

A character which has participated in a mini game with enabled ranking
statistics could not be deleted. The database rejected it with

  Npgsql.PostgresException 23503: update or delete on table "Character"
  violates foreign key constraint "FK_MiniGameRankingEntry_Character_CharacterId"

MiniGameRankingEntry is a member of neither the character nor the mini game
definition aggregate, so the model generator doesn't emit a delete behavior
for its references. The entity was registered without any additional
configuration, so Entity Framework fell back to no action for these optional
relationships, which the database translates into a restricting foreign key.

Both references are now configured with a cascading delete, matching the
behavior of the other references to a character. With that, all seven
relationships pointing to Character delete their dependents.

This affects both deletion paths: the one of the player
(DeleteCharacterAction) and the one of an administrator, who can remove a
character from the account in the admin panel.

The cascade on the mini game definition is deliberate and part of the same
defect: deleting a definition in the admin panel ran into the very same
restriction. It does mean that the ranking history of a mini game is dropped
together with its definition.

Reported in issue 796.

(cherry picked from commit a391bdedbbd3a36ccb37124125bd7ede4f851dca)

src/Persistence/EntityFramework/EntityDataContext.cs

@@ -44,7 +44,7 @@ public class EntityDataContext : ExtendedTypeContext
         modelBuilder.Entity<Model.AttributeDefinition>();
         modelBuilder.Entity<ConnectServerDefinition>();
         modelBuilder.Entity<ChatServerDefinition>();
-        modelBuilder.Entity<MiniGameRankingEntry>();
+        modelBuilder.Entity<MiniGameRankingEntry>().Apply();
         modelBuilder.Entity<GameServerDefinition>(entity =>
         {
             entity.Property(e => e.PvpEnabled).HasDefaultValue(true);