GLib registers number->string value transforms (meaning that
number-valued properties like NMSettingVlan:id or NMSettingWired:mtu
get loaded into their NmtNewtEntries correctly), but not the
corresponding string->number transforms (meaning changes made in the
entries don't get propagated back to the settings, and due to
http://bugzilla.gnome.org/show_bug.cgi?id=726574, there's no warning
about this). Fix this by registering our own transforms.
If you launched nmtui directly into the editor for a specific
connection, it would hang with a blank screen when you quit.
Fix this by changing the way startup works a bit, and have the created
toplevel NmtNewtForm get returned all the way to nmtui.c, which can
then connect to the "quit" signal on it and quit (rather than having
the different subprograms trying to guess whether they're supposed to
quit-on-exit or not).
We were using g_utf8_strlen() to measure strings for layout, but that
counts combining marks too, and also fails to deal with "fullwidth"
(ie, double-width) CJK characters.
Add a new utility function to do a better job of this (based on code
from vte), and use it everywhere.
"Cancel" didn't really make sense here, but changing it to "Quit" is
also weird because if you were going to use the "OK" button you'd have
to tab past "Quit" first... So make it be an option in the menu
instead.
