v1.0.0-preview2

Incremental improvements from preview1, still preparing for a GA release in the future. We've added the following surface area:

• Built support for the InstallationTemplate type.
• Added the interface InstallationAdapter which offers a contract for saving an Installation to a backend.
• Offer an alternate NotificationHub.initialize method which accepts a custom InstallationAdapter, instead of Notification Hub credentials.
• Provide callbacks for success and failure to save a Installation to the back-end.
• Remove dependency on Android Volley.