Re-create tray menu properly

[hluk]

Methods in QMenu (e.g. clear(), removeAction()) can remove separators in TrayMenu. So separator members needs QPointer and needs to be recreated if needed after they're destroyed.

Do not delete TrayMenu object in MainWindow::createMenu(), just call QMenu::clear(). Create TrayMenu, set it as context menu for tray and connect signals in MainWindow contructor.