Revert "removed FFMpeg mocking"

This reverts commit 83f0f0433210e1c3887c803a0603c26afc7f14d8.
Revert "added ffmpeg installation"

This reverts commit f609f9f28556ccd130f9c5d4f5f48a3a7ccf15fe.
simplified mimeTypes
improved validator tests
added ConstraintValidatorFactory
added docs