- Added images and text within \raw HTML tables to remove
  the default background and size restrictions.
- Replaced the controls gallery example screenshots with
  the latest ones.
- Added a screenshot of the Qt WebEngine nano browser example
- Fixed a few typos

Change-Id: Ie0d03916db98ef0ad88e6f92e51177a5a8260c9a
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>

Added high-level intro text about the important features in Qt 5.x
so that the reader will get a glipmse of these features in the intro
page.

Task-number: QTBUG-33596
Change-Id: I286e6a32d1cf5e4a7e3c5f7c08e6757d7b3b592c
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@digia.com>