Deprecate A0APIClient & A0IdentityProviderAuthenticator singletons

[hzalaz]

Now there is only one interface to use Lock which is the class A0Lock. Instead of creating a VC or using A0APIClient directly, the user should need to create a A0Lock instance and ask it for either the client or VC.

let lock = A0Lock()
let controller = lock.newLockViewController()
let client = lock.apiClient()

All the operations of the A0IdentityProviderAuthenticator are now handled directly in A0Lock.