map: use Item instead of Rectangle in MapWidget.qml

The root element is now an Item and also doesn't have explicit
anchors and dimensions as these will be handled by the parent:
- on desktop: a QQuickWidget
- on mobile: any QML based QQuickItem

Signed-off-by: Lubomir I. Ivanov <neolit123@gmail.com>

mobile-widgets/qml/MapWidget.qml

@@ -2,12 +2,7 @@ import QtQuick 2.0
 import QtLocation 5.3
 import QtPositioning 5.3
 
-Rectangle {
-	id: mapParent
-	anchors.fill: parent
-	width: 512
-	height: width
-
+Item {
 	Plugin {
 		id: mapPlugin
 		name: "esri"