FS-7519: WIP break mod_av into mod_avformat, moving to libav.org API

Tested with libav 11.3
./configure --prefix=/opt/av --enable-shared --enable-pthreads --enable-gpl --enable-version3 --enable-hardcoded-tables --enable-avresample --host-cflags= --host-ldflags= --enable-libx264 --enable-libmp3lame --enable-libvorbis --enable-libvpx --enable-libfaac --enable-libspeex --enable-nonfree --enable-vda

WIP av file interface, kind of works, need further tweak & cleanup

src/mod/formats/mod_avformat/Makefile.sample

+LOCAL_LDFLAGS=-L/opt/av/lib -lavformat -lavcodec -lavutil -lavresample
+LOCAL_CFLAGS=-I/opt/av/include
+LOCAL_LIBADD=
+
+BASE=../../../..
+include $(BASE)/build/modmake.rules