Add changes file for 5.8.0

Change-Id: I27724f6108936aadb93ceee4bd526f0bfedc0950
Reviewed-by: Antti Määttä <antti.maatta@qt.io>

dist/changes-5.8.0

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+Qt 5.8 introduces many new features and improvements as well as bugfixes
+over the 5.7.x series. For more details, refer to the online documentation
+included in this distribution. The documentation is also available online:
+
+  http://doc.qt.io/qt-5/index.html
+
+The Qt version 5.8 series is binary compatible with the 5.7.x series.
+Applications compiled for 5.7 will continue to run with 5.8.
+
+Some of the changes listed in this file include issue tracking numbers
+corresponding to tasks in the Qt Bug Tracker:
+
+  https://bugreports.qt.io/
+
+Each of these identifiers can be entered in the bug tracker to obtain more
+information about a particular change.
+
+General
+-------
+
+ - Greatly improved test coverage
+ - Added more documentation
+ - Fixed large number of bugs across all of Qt 3D
+
+Render
+------
+
+ - Texture system reworked to improve sharing of textures on the backend
+   and to minimize uploads to the GPU.
+ - Do not mirror texture coordinates or textures by default.
+ - Uniform handling system overhauled to remove usage of QVariant on the
+   backend.
+ - QRenderCapture framegraph node added to allow read back of the write
+   framebuffer to a QImage.
+ - Improved parallelisation of several job types.
+ - Improved parallelisation of OpenGL submission thread with building the
+   next frame.
+ - QObjectPicker is now also able to pick back facing triangles.
+
+Input
+-----
+
+ - Added QAxisAccumulator to allow tracking and integration of QAxis values
+   by treating the axis values as velocity or acceleration values.
+ - Added concept of proxy devices to allow new device plugins to easily
+   enumerate axes and buttons.
+
+Extras
+------
+
+ - Various fixes to the geometry attributes