I have had CO2 come out of solution that worried me before that it was early stage of an infection, but it was way less than what is shown in your picture. i think there is a good chance you have a wild bug growing in there....that is just too much white stuff for a beer nearly 20 days in. an ale yeast should be all wrapped up by then as a general rule. how was your cleaning and sanitation before primary and probably more important when transferring to secondary? for a simple beer like a summer ale, i would strongly suggest not transferring to a secondary, just give it 2 weeks or so in primary and once fermentation is complete and hydrometer reading steady, go ahead an package. one less opportunity to pick up something in your beer.