Salesforce sdk manager

A few different items here:

- `SFHybridViewConfig` is now inherited from a new `SFSDKAppConfig` class in `SalesforceSDKCore`.
- `SalesforceSDKManager` has been updated to have an optional `appConfig` property, which it will use to configure the basic app settings, if present.
- The hybrid AppDelegate has been updated to use `SalesforceSDKManager` to authenticate before launching into the hybrid loading. 
- `SFHybridViewController` has been updated to expect pre-authentication via `SalesforceSDKManager` (and fail fast if it hasn't happened).
- The hybrid app delegate pattern has been updated to be more like the native one, with an initial view before launch.

I'm not sure about that last one.  It might be better to just initialize the window without having an initial view.  Let me know what you think.