facebook share changes and twitter fix

facebook deprecated share functionality it does only meta level image reading ang titles. 
facebook dialog feed supports same function it requires facbook appid. 
refer the link: https://developers.facebook.com/docs/sharing/reference/feed-dialog/v2.1  
issue no: #33 
Added twitter via and image sharing for twitter. #43 

Added redirect url for facebook. #28 

https://github.com/huacnlee/social-share-button/blob/master/app/assets/javascripts/social-share-button.coffee#L11

You can use ``appkey` attiburte