check for needed version of libavcode, libavformat and libavutil

Summary:
check for needed version of libavcode, libavformat and libavutil

modify FindFFmpeg.cmake to better handle the components of ffmpeg and
allow to check the version of a component

ask for the versions of each component in the 3.1 version of ffmpeg

versions check do not work, so we manually checks that AVstream
structure has codecpar member

Test Plan: the check for codecpar member in AVStream structure works fine

Reviewers: romangg, adridg, jriddell

Reviewed By: jriddell

Subscribers: jriddell, kde-frameworks-devel, Baloo

Tags: Frameworks, Baloo

Differential Revision: https://phabricator.kde.org/D13302