Add icon to example desktop files

# Please enter the commit message for your changes. Lines starting
# with '#' will be ignored, and an empty message aborts the commit.
# On branch pkg-fremantle
# Your branch is ahead of 'origin/pkg-fremantle' by 1 commit.
#
# Changes to be committed:
#   (use "git reset HEAD^1 <file>..." to unstage)
#
#	modified:   debian/desktop/qt-components-calculator.desktop
#	modified:   debian/desktop/qt-components-gallery.desktop
#	modified:   debian/desktop/qt-components-pages.desktop
#	modified:   debian/desktop/qt-components-quiz.desktop
#	modified:   debian/desktop/qt-components-widgetgallery.desktop
#	new file:   debian/icons/qt-declarative.png
#	new file:   debian/qt-components-dev.postinstall
#	modified:   debian/qt-components-examples.install
#	modified:   debian/rules
#
