Improve account window

sflphone-gtk/src/accountwindow.c

sflphone-gtk/src/dbus.c

sflphone-gtk/src/druid.c

sflphone-gtk/src/druid.h

sflphone-gtk/src/sflphone_const.h

src/account.h

src/iaxaccount.cpp

src/iaxvoiplink.cpp

src/iaxvoiplink.h

src/managerimpl.cpp

src/sipaccount.cpp

src/sipvoiplink.cpp

src/sipvoiplink.h