Adds placeholders to get members at a specific rank

[EarthCow]

Adds placeholders to get the member(s) at a specific rank. If there are multiple with the same rank then they are all returned separated by commas. Closes #537

• %betterteams_owners% - Gets the owner(s) for the team that the viewing player is a member of
• %betterteams_static_owners_Supers% - Gets the owner(s) for the team "Supers"
• %betterteams_admins% - Gets the admin(s) for the team that the viewing player is a member of
• %betterteams_static_admins_Supers% - Gets the admin(s) for the team "Supers"
• %betterteams_defaultmembers% - Gets the default member(s) for the team that the viewing player is a member of
• %betterteams_static_defaultmembers_Supers% - Gets the default member(s) for the team "Supers"

[EarthCow]

I just realized #537 mentions a list for admins and members as well. I'll add those later.

[booksaw]

Thanks for all the pull requests, it is incredibly helpful. I will have a proper look hopefully tomorrow (and hopefully finally publish the update). One thing I noticed from a quick glance is that you could instead use. It would not have any performance difference as it does the same code in the backend, it just may be worth using the utility method in case for some reason something changes in the future.

 List<TeamPlayer> users = team.getRank(PlayerRank.OWNER);

As seen here: https://github.com/booksaw/BetterTeams/blob/7e507ffce087e64e01c4e03d5b6132e539aa0d26/src/main/java/com/booksaw/betterTeams/commands/team/InfoCommand.java#L86

[EarthCow]

Thanks and sorry as I did not see the method before, but I should have.