Added getOnlinePlayersFromNation function for API use

[cortageus]

Description:

I added a getOnlinePlayersFromNation function to help improve efficiency of checking online players from a nation. Right now you have to manually comb through every single player in a nation and check if "isOnline" is true. I am in a nation with around 500 players and with sending 1 request per second it takes around 8.5 minutes to get a list of only around 12 players. The API also cannot handle shorter intervals as it returns an HTTP 429, "Too many requests." If this gets approved I plan on sending another pull request in the API repo.

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New Nodes/Commands/ConfigOptions:

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Relevant Towny Issue ticket:

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• I have tested this pull request for defects on a server.

By making this pull request, I represent that I have the right to waive copyright and related rights to my contribution, and agree that all copyright and related rights in my contributions are waived, and I acknowledge that the TownyAdvanced organization has the copyright to use and modify my contribution under the Towny License for perpetuity.

[Warriorrrr]

This repository unfortunately does not accept PRs, as this is just our fork of towny with some minor changes on the fork branch. The TownyAPI class also already has the getOnlinePlayersInNation method, which means this extra method isn't needed.