Adding passcode-related category to UIApplication

Ran into an issue with passcodes not working in the latest hybrid SDK.  The reason is that hybrid Mobile SDK apps used to use `SFApplication` as their `UIApplication` class, to get user event information to determine inactivity.  This designation was configured in `main.m`.  Cordova now owns `main.m`, so we lose the `SFApplication` configuration, and things blow up from there.

Similar to `AppDelegate+SalesforceHybridSDK`, I added `UIApplication+SalesforceHybridSDK`, which implements the methods that `SFApplication` would have otherwise overridden.
This isn't my favorite thing in the world, but you can't declare member variables in categories.  Since `UIApplication` is going to be a singleton anyway, this is functionally equivalent.