Added example to move, resize, rotate and skew

Use goocanvas-3.0 to continue developing on gtk 3

This was the warning, with gcc 7:

/home/murrayc/checkout/gnome/goocanvas-2.0/src/goocanvas.c: In function ‘goo_canvas_crossing’:
/home/murrayc/checkout/gnome/goocanvas-2.0/src/goocanvas.c:3240:3: warning: this ‘if’ clause does not guard... [-Wmisleading-indentation]
   if (event->window != canvas->canvas_window)
   ^~
/home/murrayc/checkout/gnome/goocanvas-2.0/src/goocanvas.c:3245:5: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the ‘if’
     if (event->type == GDK_LEAVE_NOTIFY
     ^~

2017-08-30  Damon Chaplin  <damon@gnome.org>

    * src/goocanvas.c: If we receive a LEAVE_NOTIFY event with a mode of
      GDK_CROSSING_GRAB or GDK_CROSSING_GTK_GRAB we finish any passive grab
      we have underway. Hopefully fixes #711709

    * demo/mv-simple-demo.c (on_rect_button_press):
    * demo/simple-demo.c (on_rect_button_press): show a dialog to test
      the grab bug fix above.

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