This clarifies redistribution conditions for contributors.

Comments in the source files refer to them. Some files are under GPL with
exceptions or LGPL with exceptions, some are BSD-licensed:

find -type f |xargs sed -n 's/.*\(\$QT_BEGIN_LICENSE:[^\$]*\$\).*/\1/p' |sort |uniq -c
    104 $QT_BEGIN_LICENSE:BSD$
    108 $QT_BEGIN_LICENSE:LGPL$

There's also one GFDL licensed file:
doc/global/qt-html-templates-offline.qdocconf

Change-Id: I924ca0649691a52e9d7641962350e6857d82f947
Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Reviewed-by: Pier Luigi Fiorini <pierluigi.fiorini@gmail.com>
Reviewed-by: Jørgen Lind <jorgen.lind@digia.com>