[BUGFIX] Set correct file extensions in ['SYS']['mediafile_ext']

The file extensions mp3, wav, mp4 and webm are added to
$GLOBALS['TYPO3_CONF_VARS']['SYS']['mediafile_ext'].

The extensions mov and avi are removed as these are not supported
by the renderer classes provided by the core.

Change-Id: I445054687fc4f56640e2455cb83f8ae30b9bbde4
Resolves: #70298
Releases: master
Reviewed-on: http://review.typo3.org/43732


Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Michael Oehlhof <typo3@oehlhof.de>
Reviewed-by: Daniel Goerz <ervaude@gmail.com>
Tested-by: Daniel Goerz <ervaude@gmail.com>
Tested-by: Michael Oehlhof <typo3@oehlhof.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>