Introduction of an activation trigger between trains in a timetable

Presently, trains can be regulated to wait for another train using the 'wait', 'follow' or 'connect' commands. However, in complex situations like shunt moves with multiple engines, it is not always possible to set up such commands in a proper way.
Using triggers between trains can avoid this problem. Using triggers, a train will remain static until it is activated by a trigger from another train. A train can send a trigger to activate another train on start, dispose or station stop (both on stop and on depart).
To set a trigger, the following commands are available.

For the train to be activated :
add $activated command in the #start field.

For the train sending the trigger :
add $activate=<train> in #note field, #dispose field or for a station stop.
For a station stop, the additional parameters /stop or /depart can be set.

Note that $activated is not possible for trains starting from a pool.