add a dex mode for Api21 style application modules
add a dex mode for Api21 style application modules

Summary: instead of dropping the dex files into the root of the apk for app modules, it should drop them into the assets

Reviewed By: bertmaher

Differential Revision: D3737997

fbshipit-source-id: ed98173aa31ce7bab2f563ec030ea87618a1e19c

facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex