Translation update: Tutorial, The Unknown (All languages)

Updated with new script `development/translate_scenario`.

NOTE: This commit lacks updated to several languages with currently
broken translation files exported from pootle (msgfmt errors).
Probably incomplete list:
- content/scenarios/The_Unknown_es.yaml
- content/scenarios/tutorial_bg.yaml
- content/scenarios/tutorial_da.yaml
- content/scenarios/tutorial_ro.yaml
- content/scenarios/tutorial_ru.yaml
- content/scenarios/tutorial_zh_CN.yaml
translate_scenario: Strip trailing newline from translation status
translate_scenario: Translate metadata

No comment about this code except that i was seriously considering to
--author someone else before committing.
translate_scenario: Py2.6 compatibility

Also make __file__ invocation more diff-safe.
translate_scenario: Hack to reuse old translation files

This should be reverted as soon as pootle is back and running.
translate_scenario: Note original scenario, add header to translated files