Adjusting the switchbutton so that the callback doesn't fire on
pageload and allowing the hidden checkbox to be found with screenreaders
and one can reference a javascript function with the
on_callback/off_callback options.

Now one can do either
  on_callback: function() { },
or
  on_callback: 'myfunction',

Signed-off-by: Robert Lyon <robertl@catalyst.net.nz>
Merge branch 'master' of https://github.com/robertlyon777/jQuery-switchButton