add gcm handler to change event details

[ShikherVerma]

after #34
on gcm client add option to recieve this , show notification
{
"to": "/topics/foo-bar",
"data": {
"type":"eventdetailchange"
"event":"bla bla event"
"timing": "20:00-23:00",
"venue": "oat"
}
}

add option in data provider to change event timing and venue.