Doc: Added the missing \brief and \image for example docs

The Qt TestLib examples are just tutorials so updated
the qdocconf to use the default thumbnail in the
Qt Creator welcome screen.

Task-number: QTBUG-41996
Change-Id: Ia04a42a92e414c97a426b6095a62621a348e7de0
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>
Reviewed-by: Martin Smith <martin.smith@digia.com>

examples/widgets/doc/src/plugandpaint.qdoc

@@ -30,8 +30,7 @@
     \title Plug & Paint Example
     \ingroup examples-widgets-tools
 
-    \brief The Plug & Paint example demonstrates how to write Qt
-    applications that can be extended through plugins.
+    \brief Demonstrates how to extend Qt applications using plugins.
 
     \image plugandpaint.png Screenshot of the Plug & Paint example
 
@@ -314,6 +313,9 @@
 /*!
     \example tools/plugandpaintplugins/basictools
     \title Plug & Paint Basic Tools Example
+    \brief A plugin providing the basic tools for painting functionality.
+
+    \image plugandpaint.png Screenshot of the Plug & Paint example
 
     The Basic Tools example is a static plugin for the
     \l{tools/plugandpaint}{Plug & Paint} example. It provides a set
@@ -499,6 +501,9 @@
 /*!
     \example tools/plugandpaintplugins/extrafilters
     \title Plug & Paint Extra Filters Example
+    \brief A plugin providing the extra filters.
+
+    \image plugandpaint.png Screenshot of the Plug & Paint example
 
     The Extra Filters example is a plugin for the
     \l{tools/plugandpaint}{Plug & Paint} example. It provides a set

examples/widgets/gestures/imagegestures/doc/src/imagegestures.qdoc

@@ -28,10 +28,13 @@
 /*!
     \example gestures/imagegestures
     \title Image Gestures Example
+    \brief Demonstrates the use of simple gestures in a widget
 
     This example shows how to enable gestures for a widget and use gesture input
     to perform actions.
 
+    \image imagegestures-example.jpg
+
     We use two classes to create the user interface for the application: \c MainWidget
     and \c ImageWidget. The \c MainWidget class is simply used as a container for the
     \c ImageWidget class, which we will configure to accept gesture input. Since we

src/testlib/doc/qttestlib.qdocconf

@@ -40,5 +40,8 @@ excludedirs += ../../../examples/widgets/doc
 
 imagedirs   += images
 
+# Add a thumbnail for examples that do not have images
+manifestmeta.thumbnail.names = "QtTestLib/Chapter *"
+
 navigation.landingpage = "Qt Test"
 navigation.cppclassespage = "Qt Test C++ Classes"

src/xml/doc/qtxml.qdocconf

@@ -40,3 +40,6 @@ imagedirs   += images \
 
 navigation.landingpage = "Qt XML"
 navigation.cppclassespage = "Qt XML C++ Classes"
+
+# Add a thumbnail for examples that do not have images
+manifestmeta.thumbnail.names = "QtXml/XML Stream Lint Example"