ADD web_widget_model_viewer

[UPD] Update web_widget_model_viewer.pot
[UPD] README.rst

web_widget_model_viewer/readme/CONTRIBUTORS.rst

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+* Lorenzo Battistini (https://takobi.online)
+* Andrea Piovesana (https://openindustry.it)

web_widget_model_viewer/readme/CREDITS.rst

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+Chair © Copyright 2020 Shopify Inc., licensed under CC-BY-4.0.

web_widget_model_viewer/readme/DESCRIPTION.rst

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+``<model-viewer>`` is a web component that makes rendering interactive 3D models - optionally in AR - easy to do, on as many browsers and devices as possible. ``<model-viewer>`` strives to give you great defaults for rendering quality and performance.
+
+See `source repository <https://github.com/google/model-viewer>`_ and `documentation <https://modelviewer.dev/>`_.
+
+The model to load is a GLTF 2.0 file format.
+
+See `<https://www.khronos.org/gltf/>`_ and GLTF overview:
+
+.. figure:: ../static/img/gltfOverview.png
+
+Many engine developers have already started transitioning to glTF 2.0 to reap performance, portability and quality benefits, including BabylonJS, three.js, Cesium, Sketchfab, and xeogl and instant3Dhub engines. glTF 2.0 is also seeing industry support by companies such as Adobe, Google, Marmoset, Microsoft, NVIDIA, Oculus, UX3D, and more as well as prominent universities such as, University of Pennsylvania and Sapienza University of Rome.
+
+"example" directory contains the GLB file of a chair, that is rendered in the following way:
+
+.. figure:: ../static/img/Eames_Lounge_Chair.gif

web_widget_model_viewer/readme/HISTORY.rst

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+12.0.2.0.0 (2020-07-14)
+~~~~~~~~~~~~~~~~~~~~~~~
+
+* [IMP] fullscreen and view redesign
+
+12.0.1.0.0 (2020-07-10)
+~~~~~~~~~~~~~~~~~~~~~~~
+
+* Start of the history.

web_widget_model_viewer/readme/USAGE.rst

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+Add ``widget="model_viewer"`` to your binary field in form view. Optionally you can set ``style`` and ``max_upload_size`` (in MB) attributes.