aggregateMenu: Ignore ellipsizable items in width-request

aggregateMenu: Ignore ellipsizable items in width-request

Some labels in the system status menu - namely network names - are out
of our control, and may thus grow the width "infinitively" unless we
restrict the menu width. So far we have been doing this by setting a
fixed width or max-width, but any value we put there might end up
being too restrictive in some locales. Instead, request a width that
fits all the labels we want to show unellipsized and use that instead
of an arbitrary limit.

https://bugzilla.gnome.org/show_bug.cgi?id=708472