I want to link two symbols, so that I can assign a 'click' action to one that plays the timeline of another.

Yes this is possible.

If you are in "symbol_1" and you want to play something inside "symbol_2"

inside symbol_1 have this: sym.getComposition().getStage().getSymbol("symbol_2").play("INSERT_LABEL_OR_TIME");

hope this helps

Add the following code to "click" handler of symbol_2

sym.getSymbol("Symbol_1").play();

You can go through actions popup to do all these kind of stuff.

http://helpx.adobe.com/edge-animate/using/whats-new-2014.html#Enhanced Actions editor