Create `PlayerHighestRanks` database entity

[myssto]

This entity will store information about a Player's highest achieved global and country rank. Each Player can own a maximum of one PlayerHighestRanks per Ruleset (similarly to PlayerRating).

• [x] PlayerHighestRanks entity created
• [x] Navigation added to existing Player entity
• [x] Relevant database migration created and tested

The entity should be structured as such:

public class PlayerHighestRanks : IUpdateableEntity
{
  public Ruleset Ruleset { get; set; }

  public int GlobalRank { get; set; }
  public DateTime GlobalRankDate { get; set; }
  public int CountryRank { get; set; }
  public DateTime CountryRankDate { get; set; }

  // FK, required
  public int PlayerId { get; set; }
  // Backwards navigation
  public Player Player { get; set; }
}

The entity should:

• Have a table named player_highest_ranks
• Have a one to many relationship with Player (Player -> PlayerHighestRanks)
  • Unique compound index of { PlayerId, Ruleset } (Max one per ruleset per player)
• Cascade delete on Player deletion

[alixdotsh]

im gonna try doing this, ill let someone know if i dont got it lol