The_Unknown: Update syntax to use logbook-data

Easier to translate that way.
Partial rewrite of scenario handling in SP menu

Not even pretending that splitting this into small chunks helps
understand any of the changes, simply because it's still horrible.

New bugs introduced due to changed scenario structure: Now require
metadata previously stored in root level to be defined in an explicit
`metadata` dictionary instead. This prevents parsing entire files
multiple times when querying difficulty, author, description and so on.

As for backwards compatibility, we need to add some currently missing
features to the new scenario translation script instead and just declare
old scenarios incompatible, providing updated versions of everything we
previously shipped. In particular, regressions in the new script are the
lack of translation for description, difficulty, and author, as well as
the completely missing translation status to be displayed in our gui.

For now, updates to the english parent scenarios are included in this
commit and updating the other languages is not possible. A new commit
running the new scenario translation script with updated translation
files from pootle should be attached to this before merging any of it.
Update string previewer to new scenario metadata structure
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