Move tooltip window hover detector to HToolTip

Having a HoverHandler covering the root ApplicationWindow causes
problems for some Qt Quick Controls with pen/touch, e.g. it's impossible
to focus a TextArea/TextField.

The HoverHandler is moved to HToolTip (since it's used for those),
targets the ApplicationWindow but is now only enabled while a tooltip is
visible.

src/gui/Window.qml

@@ -10,7 +10,6 @@ ApplicationWindow {
 
     // FIXME: Qt 5.13.1 bug, this randomly stops updating after the cursor
     // leaves the window until it's clicked again.
-    readonly property alias hovered: windowHover.hovered
 
     readonly property bool hidden:
         Qt.application.state === Qt.ApplicationSuspended ||
@@ -85,8 +84,6 @@ ApplicationWindow {
 
     Utils { id: utils }
 
-    HoverHandler { id: windowHover }
-
     HLoader {
         anchors.fill: parent
         source: py.ready ? "" : "LoadingScreen.qml"