helpers that do not relate with xmpp, belong to helpers.py not to common/gajim.py. if they have gtk they belong to gtkgui_helpers. also use those allover

fix a nice thought of travis to work ok with talkig to 2 or more resources the same time [do not show account name then]

that connection is already established

established

show gajim.png image instead of STOCK_APPLY image cause in many theme (gnome one) it's too small and it looks ugly

handle correctly when server return answer to register request when we create a new account. Fixes #1725