MainWindow / MapSettings - Undo stack wip

- get rid of pointer onto MapSettings, using a link to mainwindow
  instead (not sure this is a better approach though, introduces
  complexity in term of relation - circular dependencies - between
  objects).

- Removing method changeMapName() because this has to be managed at the
  saveMapSettings() level.
Merge remote-tracking branch 'upstream/master'
move activated to doubleClicked