Refs #19736 Forum; Refs #3929 Forum; now media converters can use avconv and flvmeta instead of ffmpeg and flvtool2, better availability on modern platforms

git-svn-id: https://svn.eionet.europa.eu/repositories/Naaya/trunk/eggs/Naaya@20911 a0171fae-0946-0410-966d-b1775066cd26