Provide auto-completion for alias-to-url properties

import QtQuick 2.0

Image {
    source: "" // this gives nice auto-completion of paths
}

import QtQuick 2.0

Item {
    property alias source: myImage.source
    Image {
        id: myImage
    }
}

import QtQuick 2.0

MyComponent {
    source: "" // no auto-completion of paths available
}