Make PLS parser more permissive.

The PLS format is not clearly specified, some rules are just assumed
and files don't always respect them.
We now only look for 'File' entries, since that's the only thing we
actually use. We ignore the Version, NumberOfEntries, Title, Length
and any other unrecognized tags.

Task-number: QTBUG-40515
Change-Id: I9c176b7b68fd1441abbd50364f88994ad5d6236f
Reviewed-by: Christian Stromme <christian.stromme@digia.com>