It is a cold day in winter, but Seapoint near Monkstown in south Dublin is heaving with sea swimmers. Emmet Savage, the chief executive of MyWallSt, is dressed warmly for the occasion as we sit on a ledge overlooking the sea to talk about his business, an investment app for do-it-yourself investors. Savage co-founded the business in 2013 with John Tyrrell, and since then he says he has created a community of several hundred thousand active investors. Rob Cumiskey, head of growth with MyWallSt, had suggested we meet not long after he joined the business in October. I had spoken…