Rename the Supported Platforms page to 'Community Supported
Platforms', link to the separately-maintained page for
platforms officially supported by The Qt Company, and update
the language on the page. Specifically,
    - Mention Qt Quick 2D Renderer as an alternative to
      running Qt Quick on OpenGL-enabled platform
    - Drop the mention of Qt Quick 1 (deprecated)
    - Replace 'Digia' with 'The Qt Company' where suitable
    - Update links to this page

Change-Id: I9affd7f5b7d13e85d6a945188b29bab64dc172f3
Reviewed-by: Venugopal Shivashankar <venugopal.shivashankar@digia.com>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@theqtcompany.com>