Updates to deal with changes to the DLNA reference content file organization

Updated convert-dlna-scaled-helper.sh.

 Everything under "Scaled Files" is now "ScaledFiles".
 Had to remove a reference to MPEG_TS_NA_544x480i2997_4x3.ts. It doesn't
  seem to exist anymore.

Added support for media files with different extensions to itemGen-scaled.sh.
 The reference content isn't consistent with the case of file extensions.

Tested with latest "DLNAContent" tree provided on 2014-07-22.