Changed GPS and automatic update buttons slots

Changed GPS and automatic update buttons slots

 - Changed GPS & auto centering signals so that actions are not
   dependent on menu button signals anymore, which weren't emitted
   at startup when states were set but didn't change from buttons
   default states

 - changed messages so that they are displayed only at startup
   and when automatic centering is disabled because user have
   scrolled the map

 - some sorting

 - changed MapEngine GPS and automatic centering settings change
   methods to public