Initial pull request to forcedotcom unstable branch of SalesforceMobileSDK-Windows

This is an early work-in-progress version of the SalesforceMobileSDK for Windows. It supports Windows 8.1 and Windows Phone 8.1.  There is no planned Windows phone Silverlight support, everything will be universal.

Current:

Universal portable library + support libraries for store, phone.
Multi account manager, account switching.
Rest support, oauth management, token refresh support.
Encryption support for settings / local storage - one example given, developer can roll their own.
Samples for store and phone include rest sample and Salesforce1 one.app container.

To-do: 

Everything else not listed such as pincode, cordova support, smart store.