[FEATURE] Leaderboard Cog

[PhlexPlexico]

Since a leaderboard is incorporated into G5V, it really doesn't make much sense for the bot to show a leaderboard. However, some people may wish to roll with the API and Bot only. So this issue is to track as a future feature to enabled a [p]leaderboard call that would get the top players in a pug. This may also require a new call from the G5API too, if it isn't there.