Add a make target for tests

We are running the existing test_mime.py. All the other tests which
are not unit tests but more examples of code one can run interactively
are moved to the example directory.

examples/cellrenderericon.py

@@ -0,0 +1,37 @@
+from gi.repository import Gtk
+
+from sugar3.graphics import style
+from sugar3.graphics.icon import CellRendererIcon
+
+import common
+
+
+test = common.Test()
+test.show()
+
+model = Gtk.ListStore(str)
+for icon in ['one', 'two', 'three']:
+    model.append([icon])
+
+treeview = Gtk.TreeView()
+treeview.set_model(model)
+test.pack_start(treeview, True, True, 0)
+treeview.show()
+
+col = Gtk.TreeViewColumn()
+treeview.append_column(col)
+
+cell_icon = CellRendererIcon(treeview)
+cell_icon.props.width = style.GRID_CELL_SIZE
+cell_icon.props.height = style.GRID_CELL_SIZE
+cell_icon.props.size = style.SMALL_ICON_SIZE
+cell_icon.props.icon_name = 'emblem-favorite'
+col.pack_start(cell_icon, expand=False)
+
+cell_text = Gtk.CellRendererText()
+col.pack_start(cell_text, expand=True)
+col.add_attribute(cell_text, 'text', 0)
+
+
+if __name__ == '__main__':
+    common.main(test)