Re-added AI vocal announcements with improvements.

Unlike before, the announcement no longer requires a huge list to work, saving up room from the string table.
They also work while streaming resources, meaning they won't overlap; this is because the resources are sent when a user joins, instead of when the AI makes an announcement and it messes up the ordering.

* There have been improvements since last time, they now have a small delay of 10 seconds, which anyone is free * to adjust.
* The help screen will now only preview the sound to the AI.
* The last announcement is saved to the AI's variables.
* There's a limit of how many words can be said in a single announcement.