Renamed itemGen-scaled.sh to odid_itemgen.sh and added --item-suffix option

The rename is to allow this script to expand its functionality beyond
 scaled content - since it can/will be used for (indexed) DLNA content without
 scaled content files. And eventually this script may be used to create
 indexes and/or decimated streams using the CableLabs indexVideo tool.

Updated the convert-dlna-scaled-helper.sh to pass through the new flag
 and to call the script by its new name.

Tested odid_itemgen.sh and the helper with and without the --item-suffix
 parameter.