Plugin support for OpenRCT2

[GingerAdonis]

@IntelOrca announced the support for plugins which should allow further customization for both single-player and multiplayer. All details can be found in this reddit post: https://www.reddit.com/r/rct/comments/g8nq60/openrct2_plugin_support_now_available/

 

I've also added a `Plugins` forum to the `Custom content` section to discuss and share plugins. https://forums.openrct2.org/forum/21-plugins/