[TIMOB-4991] Android: Call module's onAppCreate method as part of application's onCreate processing

The Urban Airship module requires some specific initialization to occur during the onCreate method of the application object. Urban Airship starts a Push Service during the application initialization AND it also registers with the BOOT_COMPLETED intent so that it gets restarted on a system reboot. This second case causes an instance of the application to be created (without starting the main activity) and it is this process startup that requires the module to be able to set the configuration options. Failure to do this causes the Push Service to throw an exception and crash. I have defined a static method in the UA module called onAppStartup(). This static method needs to be called from the application's onCreate method. There have been a couple of ideas surrounding this. One that I have implemented and tested uses reflection to query if the custom module contains the onAppCreate method and invokes it if found. The current implementation does the reflection at run time -- it may be possible to do the reflection at build time and insert the code into the onCreate method only if needed. Another proposed idea is to add an attribute to the tiModule.xml file to indicate that during the code generation phase it should insert a call to the module's onAppCreate method. It would then be required by the module developer to ensure that this method is implemented. Another proposed idea is to expose a new annotation, something like @Ti.onAppCreate, that would used to identify a method to be called from the application's onCreate. The requirement basically is to call a static method called 'onAppCreate' in the module if-and-only-if that method is defined in the module. The Urban Airship module has been updated to include this method.