Add ffmpeg and dependent packages as well as LD_LIBRARY_PATHs (#3276)

This change adds mp4 support confirmed on Heroku-16 stack.

.profile

@@ -0,0 +1 @@
+LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/app/.apt/lib/x86_64-linux-gnu:/app/.apt/usr/lib/x86_64-linux-gnu/mesa:/app/.apt/usr/lib/x86_64-linux-gnu/pulseaudio

Aptfile

@@ -1,2 +1,5 @@
 protobuf-compiler
 libprotobuf-dev
+ffmpeg
+libxdamage1
+libxfixes3