we now show a happy dialog on nick conflict asking (and even proposing new nick); also refactor code and add a new gtkgui helper

we now cache avatar, so we only ask once. TODO: ask, store and show in roster; TODO2: on new sha reask vcard to get new avatar

mouseover avatar now show avatar in normal size; adding some FIXMES. Yann please look at the return 0 one

remove the contact_mutual_removal advanced option and add a checkbutton in remove_contact dialog to ask if we want to remove both subscriptions

refactor to allow changing our nick after nick conflict but first #967 needs to be fixed so I can test