Implement the API Client for Mobile

[jsturtevant]

Use the following blog post for guidance: http://arteksoftware.com/resilient-network-services-with-xamarin/

• add authentication code for accessing list (azure b2c)
• add api call using refit
• setup basic caching
• add platform specifc handlers
• prioritize network calls
• check for connections via plugin
• retries via polly