Skipping the bitmap pool if the image to be decoded is a GIF

Exposed a method to return the type of the image to be decoded. For now supports GIF, APNG, PNG, JPEG and UNKNOWN

We skip the bitmap pool if the image is a GIF because of : 

https://groups.google.com/forum/#!msg/android-developers/Mp0MFVFi1Fo/e8ZQ9FGdWdEJ