We were converting markdown to HTML every time we saved a record, which
has the same problems as sanitizing HTML before saving it to the
database, particularly because the body of a legislation draft is stored
in a translations table.
Performance-wise this isn't a problem: converting a text with more than
200_000 characters takes about a milisecond on my machine.
Note we need to modify a migration generated by globalize, since the
method `create_translation_table!` would fail now that we don't define
`translates :body_html` in the model.
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