Option to Disable Tray

[hluk]

There should be an option to completely remove the application icon from tray.

Tray will not be used if any of these are true:

• user implicitly disabled tray,
• tray is not available (QSystemTrayIcon::isSystemTrayAvailable() == false),
• Qt doesn't create tray icon correctly (e.g. there is no tray icon in Qt 5 when using some window managers on X11).

In the latter two cases the option should be always enabled and hidden.

Window should be just minimized instead of closed if tray is disabled. Other option is to completely hide window but user should be able to open the window just by running the application again.

Closing minimized window (usually from context menu right clicking on a panel with windows) should close the application.