XLIFF filter code protection of target parts

[Clément Mouchet]

We can receive target content that needs the same code protection as the source.

This enhancement add the ability to protect target content when the number of codes is balanced between source and target. This allows for instance to receive content already translated that contains unprotected codes in both source and target.

It’s not desirable to protect codes if the source and target are not balanced though, so in that case, the target will be left untouched (current behaviour) and a warning will be logged.

[Clément Mouchet]

PR opened https://bitbucket.org/okapiframework/okapi/pull-requests/316