amd support + optional callback instead of tracking closed state

[mente]

Hello,

This PR adds amd support and optional callback for finished authorization, instead of tracking closed state. Example of response instead window.close():

<script type="text/javascript">
window.callback({user: avasilenko, token: 123});
</script>

Regards,
Alex

[mente]

added elegant callback injection as seen on stackoverflow

[mente]

appeared that direct callback injection had problems if there was any page loading instead of direct redirect.
Latest commit assumes following call:

<script type="text/javascript">
window.opener.oauthCallback({user: avasilenko, token: 123});
</script>