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>