Add state attribute to target tag of xliff at export time

If you checkout a translation from translate5 with standard xliff 1.2 files, there is no state set to the target tag.

This leads xbench to consider all segments as untranslated.

To solve this, a state attribute will be added to each target tag:

• translated for everything with a target, if the processing state in translate5 is translated or translated, auto
• signed-off for everything with processing state in translate5 is reviewed, "reviewed, auto", reviewed untouched, reviewed unchanged, reviewed unchanged auto
• final for everything with a target not empty, if the processing state is "2. Review" or "2. review auto" or any PM-review state
• needs-translation for everything with processing state "not translated"
• needs-l10n for everything with processing state "pre-translated"

In addition, please add the "tool" tag of the xliff spec 1.2 to the xliff and set it to "tranlate5 plus version number".