Declarative dialog improvements for the non-Window use case

Platforms like Android and EGL don't support multiple top-level
windows, so we have to avoid trying to use widget-based dialogs
(because a widget dialog on top of a scene graph will result in a
second window), allow the QML dialog to be an Item, and decorate it
to look like a window.

Task-number: QTBUG-31898
Change-Id: I9af049f3265188e8be677a05a8bc6d1699b4cd00
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@digia.com>
photosurface: add C++ boilerplate launcher; open button

Creator refuses to build it for Android otherwise, and this is a good
demo for tablets.  Also added a button to re-open the FileDialog.

Task-number: QTBUG-31898
Change-Id: I9f90de316fcaa2679484f8a875737ffafa774f31
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>
Reviewed-by: Venugopal Shivashankar <venugopal.shivashankar@digia.com>
Undo presumably accidental line deletion

Change-Id: I7ddb3ef9b45cfb95c48c2060dc62acd4ed9d64f9
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Switch to non-streaming version of qWarning()

Allows us to drop the qdebug.h include in a public and frequently used
header.

Change-Id: I2cb05fbec6298ba600020db684e9eea4093ce663
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Christopher Adams <chris.adams@jollamobile.com>
QtQuick.Dialogs: sync the docs with the implementation

We've been using URLs instead of strings for some time now, just
forgot to change the docs until now.

Task-number: QTBUG-31847
Change-Id: I49a42282aeefb95e4d367397e2f290f4af65687e
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
Reviewed-by: Venugopal Shivashankar <venugopal.shivashankar@digia.com>
QtQml: document QQmlExtensionPlugin::baseUrl

It was added here https://codereview.qt-project.org/#change,47532
without documentation.  Also updated \since because for now qdoc
seems to interpret \since 5.0 as QtQml 5.0.

Task-number: QTBUG-31928
Change-Id: I652e9471f1ad8e83b355bffc8498a6565dc9aa2b
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
Reviewed-by: Martin Smith <martin.smith@digia.com>
FileDialog.folder property should also be a QUrl, for consistency

In QtQuick we never use plain file paths, because URL is more general.
Also use const references for string and URL setters, and fixed the
dependency between the FolderListModel's folder, the field for editing it,
and the folder property of the AbstractFileDialog.

Change-Id: I6e965b80b73d4eb2473712a4f4d4f816b768d802
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>
Merge remote-tracking branch 'origin/release' into stable

Change-Id: I140852ef7fbbfe303dac620af5e6eba5ee3a4b02