add Android.mk files to enable building in tree

  to use the library in your app, edit the apps Android.mk and do EITHER 1 OR 2

   1. build from source (recommended)

        add the following line
        LOCAL_STATIC_JAVA_LIBRARIES := ListViewAnimations

   2. use prebuilt jar (adding a provision, but not recommended to use this way)

        add the following line
        LOCAL_STATIC_JAVA_LIBRARIES := listviewanimations_prebuilt

Signed-off-by: Arnav Gupta <championswimmer@aokp.co>