Refactor logon API to use block

- Add new logonWithUnsername:password:responseCallback method and
call it back when appropriate when parsing responses from server
- Start refactor of auth state vars towards a single enum unification (create temporary
_setAuthState internal methods)
- Move SRP parsing methods to meteor client parsing category
- Mark logonWithUsername:password:, sendWithMethodName:parameters:notifyOnResponse:, and sendWithMethodName:parameters as deprecated
- Upgrade iOS platform in Example app
Unify auth state variables
Meteor client changes to loggingIn state correctly.
Update example app to use block based logon API.

- Remove implementation of outdated DDPAuthDelegate.
Update example todo app meteor to 0.6.6.3