Don't load it from the image sample directory, this doesn't necessarily
work under Unix if the image sample hadn't been built.
Just embed an XPM image directly into the sample, this is good enough
for demonstration purposes.
Don't request touch event generation for all windows by default, this
has an inherent overhead and is not needed for 99% of the application
windows, so require calling EnableTouchEvents() explicitly to do it
instead.
Note that this requires properly initializing gesture recognizers in
wxOSX now that they're not always allocated, otherwise releasing them
when destroying the window would crash.
