add a pulse for whatsapp accounts #359

This adds an interval that sends presence requests for every chat every 30 seconds to keep the connection to whatsapp alive.
I tested it on my Geeksphone Peak and I can say that I wasn't disconnected the entire day. I was most of the time on wifi and the battery usage didn't increased, but I'll do future tests on mobile data, just to make sure.
improvements

some improvements for the WhatsApp pulse:
	- don't request presence status for groups
	- keep requesting even when we have no connection, only stop if the account is disabled
request all states at once
clean up
Merge pull request #550 from TitanNano/wapp-connection-fix

add a pulse for whatsapp accounts #359