CMake: add an option to deploy dependencies

[cchampet]

To automatically create an independent bundle (with no need to set env to run).

TODO:
1 - add a CMake argument AVTRANSCODER_DEPLOY_DEPENDENCIES
https://github.com/tuttleofx/TuttleOFX/blob/develop/CMakeLists.txt#L16

2 - set rpath of libavtranscoder

3 - update Travis (no need to archive several directories of libraries)
https://github.com/mikrosimage/avTranscoder/blob/develop/.travis.yml#L87

[cchampet]

Since avtranscoder only depends on ffmpeg/libav, this is not a big deal to manage its dependencies. And the problem is more the dependencies of ffmpeg/libav (libx264, libfdk-aac...). So this is not a good idea the copy ffmpeg/libav libs to INSTALL_PREFIX/lib.

But maybe there is a way to list dependencies of a library. It will enable us to copy all libs to INSTALL_PREFIX/lib.