centralize and fixup example sources install targets

This follows suit with aeb036e in qtbase.

Change-Id: Ie8580d0a1f38ab9858b0e44c9f99bdc552a1752a
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: hjk <qthjk@ovi.com>

examples/multimedia/video/doc/src/video-qml-paint-rate.qdocinc

@@ -0,0 +1,43 @@
+The QML painting rate is calculated by the FrequencyMonitor class, which
+turns a stream of events (received via the notify() slot), into an
+instantaneous and an averaged frequency:
+
+\quotefromfile video/snippets/frequencymonitor/frequencymonitor.h
+\skipto class FrequencyMonitor : public QObject
+\printuntil Q_OBJECT
+\skipto Q_PROPERTY(qreal instantaneousFrequency
+\printuntil averageFrequencyChanged)
+\skipto public
+\printuntil :
+\dots
+\skipto static void qmlRegisterType
+\printuntil ;
+\skipto public slots
+\printuntil notify();
+\skipto };
+\printline };
+
+The FrequencyMonitor class is exposed to QML like this
+
+\quotefromfile video/snippets/frequencymonitor/frequencymonitordeclarative.cpp
+\skipto FrequencyMonitor::qmlRegisterType
+\printuntil }
+
+and its data is displayed by defining a QML item called FrequencyItem, like this:
+
+\quotefromfile video/snippets/frequencymonitor/qml/frequencymonitor/FrequencyItem.qml
+\skipto import FrequencyMonitor
+\printuntil id: root
+\dots
+\skipto function notify
+\printuntil id: monitor
+\skipto onAverageFrequencyChanged
+\printuntil {
+\skipto averageFrequencyText
+\printuntil /^\}/
+
+The result looks like this:
+
+\image video-qml-paint-rate.png
+
+