Adding empty wp8 project

Using the panorama template.
Creating models project
First cut at OAuth flow
Creating SplitwiseProxy

The SplitwiseProxy is a singleton to assist with sharing a single
RestClient across XAML page loads through the app. The Login.xaml page
will decorate the proxy's RestClient with authentication information as
soon as the application loads.
Saving credentials to isolated storage

When a login using OAuth is successful, save the tokens and token secret
into isolated storage so that we can fetch it the next time the app is
run. Need to check the expiration policy for the splitwise OAuth tokens.