Add new API method "getAPIs()"

As per http://forums.bukkit.org/threads/bukkit-getserver-getname-and-a-brainstorm.153724, I'm pushing a change to have a way for downstream server implementations to pass what APIs the server implements without having the Bukkit API fragment between different implementations.

If a plugin wants to know if the Server implements the Forge API, for example, the plugin would call Bukkit.getServer().getAPIs() and parse the String[] array for "Forge". Quite simple, no?

This PR will not break the current API in any way. All past plugins will work correctly.