implementing issue 28. commit before test on dev1 server. (10)

28) add share icons to api_gift (one icon for each api provider)
    OK for facebook, google+, linkedin, Pinterest, twitter and vkontakte.
    todo:  add ajax spinner while fetching share url from server. Normally quick, but server is slow and small.
    todo: change error handling in get_share_gift_link. Do not use alert. Use ajax error table under gift links
    todo: add ajax spinner when fetching deep link from server
    todo: gifts/show with deep link - reuse deep link in new share without refetching deep link from db
    todo: check http://developer.sharethis.com/Web_Share_API