Doc: Changed layout to use the empty spaces efficiently

- 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>
Doc: Update licensing documentation

Add information about the following licenses:
   - libjasper version 2.0 (qtimageformats)
   - Mesa llvmpipe software rasterizer

Also, remove the use of '\generatelist legalese' command
from the licensing docs, as it results in duplicate entries.

Task-number: QTBUG-42173
Task-number: QTBUG-42711
Change-Id: Ie8a60e01a597fa4c28adf251e8fecd222d3de468
Reviewed-by: Sami Makkonen <sami.makkonen@digia.com>
Reviewed-by: Martin Smith <martin.smith@digia.com>