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.
let's keep in our mind to add it in the protocol [itself](https://github.com/aerogear/aerogear-ios-http/blob/master/AeroGearHttp/AuthzModule.swift#L23)