Update SDK Templates to wrap MainView in a Window item

[Michael Zanetti]

Currently, like 99% of the apps don't work well on windowed environments in a sense that they neither set preferred/minimum/maximum sizes, or window titles etc. Currently MainView does not support those things (and it'll be hard to add since we're talking about everything a "window", so the currently best thing we can do is to wrap the MainView in a Window item.

The new templates should be something like

import QtQuick 2.4
import QtQuick.Window 2.2
import Ubuntu.Components 1.3

Window {
    width: units.gu(70)
    height: units.gu(70)
    visible: true
    title: i18n.tr("My cool app's name")

    minimumWidth: units.gu(40)
    minimumHeight: units.gu(40)

    MainView {
        anchors.fill: parent
        applicationName: "foo.bar"
        AdaptivePageLayout {
            ...
        }
    }
}

This should "just work" in qmlscene based templates. In templates that are based on a main.cpp, the cpp code needs to be changed into something like:

int main(int argc, char* argv[]) {
    QGuiApplication app(argc, argv);
    QQmlApplicationEngine engine;
    engine.load(Qurl("qrc://Main.qml"));
}