MediaModelFactory.findPart moved to SmilHelper for use in both places.

findPart updated to include looking in ContentId even if the "src" does not have the cid: prefix. Noticed from a Stock GS4.
SmilHelper now has a fixup(...) method which removes duplciate parts.

Change-Id: Idf817f92f6afd8395faeaa6faf2150d4b642a0c0
Merge branch 'jb-4.3' into jb-dev