Replace RestKit with Alamofire and ObjectMapper

[jawwad]

We don't need RestKit since we are not using CoreData and should move to a more modern serialization library.

We should be using the following:

• https://github.com/tristanhimmelman/AlamofireObjectMapper (which internally uses https://github.com/Hearst-DD/ObjectMapper)
• https://github.com/Alamofire/Alamofire
• https://github.com/Moya/Moya

[kthomas]

Paved the way for this with recent refactor of ApiService.

This is probably pretty manageable task in terms of time/complexity and could possibly go in alongside the Model id refactoring.