Open id connect

@cvasilak I've added the method login to allow OpenID Connect login. would you mind reviewing?

If you want to test it with real app, see:
https://github.com/corinnekrych/aerogear-ios-cookbook-1/tree/AGIOS-287
with this realm config:
https://github.com/corinnekrych/aerogear-backend-cookbook-1/tree/AGIOS-287.SharedShoot.openIDConnect

Note: I haven't finish demo implementation yet. Need to talk to Andrea to make it nicer and display shoot images before submitting PR.
not sure and possible miss something, but should this be introduced in the sense of since there is a gateway method ```login()``` so the user know what is doing, we can simple invoke the claims request and in the process eliminate the following in the configs and simple set them straight

```
  userInfoEndpoint: isOpenIDConnect ? "<url>" : nil,
```