[TIMOB-24650] Android: Add activityEnterTransition/activityExitTransition support to Android 4.x

*Summary:* We plan on deprecating the Ti.UI.Window "activityEnterAnimation" and "activityExitAnimation" properties in favor of the following new activity transition properties: * activityEnterTransition * activityExitTransition But we can't deprecate the older animation APIs since the above transition APIs are currently only supported on Android 5.0 and newer OS versions... and Titanium still supports Android 4.x devices. Because of this, developers are still forced to use the old animation APIs for consistent support on all Android OS versions. *Recommended Solution:* Add support for Titanium's "activityEnterTransition" and "activityExitTransition" properties on Android 4.x by replicating this feature via the Activity.overridePendingTransition() method, like how it works for the existing/older animation properties. It is okay for the other transition properties, such as "activityReturnTransition", to be ignored on Android 4.x. The new transition properties shall be favored over the older animation properties in case both are provided to the createWindow() function. After implementing the above, usage of the "activityEnterAnimation" and "activityExitAnimation" should log a warning that they are deprecated and recommend to the developer to use "activityEnterTransition" and "activityExitTransition" instead. The documentation for Ti.UI.Window (link below) will need to state that the Android animation properties are deprecated as well per [TIMOB-20498]. http://docs.appcelerator.com/platform/latest/#!/api/Titanium.UI.Window