AI trains can trigger location events

Allow AI trains to be able to trigger location events, not just the player train. A line could be inserted in an activity location event that says when a certain AI train reaches a location, an event will be triggered. This would be useful for the player to receive a message or hear a sound when an AI train has reached a location. For example, an AI train could "call on the radio" (trigger a sound file) when they pass the location event to let the player know where they are at. This is very prototypical. This would also be a good temporary way to implement detectors. Ideally, an activity event could have a line inserted that will allow it to be triggered by multiple AI trains by listing out all AI service names that can trigger the event. This could possibly be expanded to beyond just location events, and include station stops, and even switching events.

Discussion: http://www.elvastower.com/forums/index.php?/topic/32620-activity-events-triggered-by-ai-trains/
Roadmap: https://trello.com/c/CkuEK8Xh/352-ai-trains-can-trigger-location-events