Doc: Move information on GPLv3-licensed modules to the Qt Modules page

Update the header for GPLv3-licensed modules in 'All Qt Modules';
clarify their description in the licensing documentation.

Use the modules page as the single source for licensing information on
specific Qt modules, and link to it from the top-level licensing page.

Change-Id: Icb1a604e1fb96f36ee41e44a519597b01306ab3f
Reviewed-by: Tuukka Turunen <tuukka.turunen@theqtcompany.com>
Reviewed-by: Sami Makkonen <sami.makkonen@qt.io>
Reviewed-by: Kai Koehne <kai.koehne@qt.io>

doc/src/legal/licenses.qdoc

@@ -45,10 +45,15 @@
           version 3 (or GNU GPL version 3).
     \endlist
 
-    \note Some specific parts (modules) of the Qt framework are not available
-    under the GNU LGPL version 3, but under the
+    Qt contains also \l {Licenses Used in Qt}{third-party code} that is licensed
+    under specific open-source licenses from the original authors.
+
+    \note For open-source licensed Qt, some specific parts (modules) are not
+    available under the GNU LGPL version 3, but under the
     \l {GNU General Public License (GPL)} instead. See
-    \l {Licenses Used in Qt} for details.
+    the list of \l {gpl-licensed-addons}{Qt modules} for details. For commercial
+    licensees, all modules are available under a single, commercial Qt
+    license.
 
     \e {Qt documentation} is licensed under the terms of the \l{GNU Free
     Documentation License (FDL)} version 1.3, as published by the Free Software
@@ -76,6 +81,7 @@
 
 /*!
     \page licenses-used-in-qt.html
+    \keyword Third-Party Licenses Used in Qt
     \title Licenses Used in Qt
     \brief Information about other licenses and third-party code used in Qt.
 
@@ -92,22 +98,6 @@
           third-party components that you are using with your application.
           Click the name of the component to see the licensing details.
 
-    \b {Modules Licensed Under GPLv3}
-
-    A number of Qt modules are only licensed under the \l{Qt Commercial License}
-    or the \l{GNU General Public License (GPL)} version 3:
-
-    \div {class="fixed"}
-    \table
-        \row \li \l {Qt Charts}
-             \li Commercial Licenses, or GNU General Public License v3
-        \row \li \l {Qt Data Visualization}
-             \li Commercial Licenses, or GNU General Public License v3
-        \row \li \l {Qt Virtual Keyboard}
-             \li Commercial Licenses, or GNU General Public License v3
-    \endtable
-    \enddiv
-
     \b {Third-party Licenses}
 
     The following table lists parts (modules) of Qt that incorporate code licensed

doc/src/qtmodules.qdoc

@@ -335,7 +335,9 @@
         \li Provides a framework to develop a Wayland compositor.
     \row
     \header
-        \li {4,1} Add-ons available under GPLv3 license
+        \li {4,1} \target gpl-licensed-addons
+                  Add-ons available under Commercial Licenses, or GNU General
+                  Public License v3
     \row
         \li \l{Qt Charts}
         \li All