MediaPlayerControls fixes & improvements

PlaylistModeItem: Mark mode property as required

The component does not make sense without it.

MediaPlayerControls: Simplify loop over elements to install event filter

MediaPlayerControls: Simplify next mode calculations using remainder operator

This is how it usually done in similar cases.

MediaPlayerControls: Use MediaPlayListProxyModel enum names instead of magic numbers

MediaPlayerControls: Copy Accessible.role and down to Repeat button from Menu button

MobileTrackPlayer: Copy checkable and checked properties definitions from MediaPlayerControls

FlatButtonWithToolTip: Hide tooltip when button's menu is open

Since they are drawn as overlay items within shared QtQuick scene, tooltips can easily overlap with menus creating frustrating user experiences. So let's integrate menu management into the button itself a bit, so that the button known when to dismiss its own tooltip popup.

MediaPlayerControls: Fix QML/JS code style

ElisaMainWindow: Mark some properties as readonly as appropriate

ElisaMainWindow: Fix QML/JS code style

MediaPlayListView: Port Connections to the new functional syntax