[TIMOB-24253] Android: Fix 'androidback' event

[garymathews]

• Fix androidback event to override default behaviour

TEST CASE

var w = Ti.UI.createWindow({backgroundColor: 'green'});

w.addEventListener('androidback', function() {
    alert('androidback pressed');
});

w.open();

JIRA Ticket

[frankieandone]

CR and FT PASS