Add translation support

• Translators get the markdown files paragraph by paragraph. It's worse than before, but there already was markup in the strings with mallard in prev. release notes.
• After changes to markdown files, ./binturong.py content-changed has to be executed.
• The generated python files have to be committed to the repository to be available for dammed lies.
• There is no language selector yet. Currently, the preferred language from browser settings wins. Maybe we can add it tomorrow.
• If we want a different system for the next release, the translated .md files can be added to the repo for 42 and the rest of this system can be removed.
• Currently, only the .md files contents are translated. The "Home" button and <title> tag are missing.

Closes #7 (closed)