Make drag-and-drop work on Chrome.

We actually want links to be drag and dropped, not text. Getting links
through text/plain was working on Firefox, but it’s non-standard.
Configuration CSS tweak for the dev website.

The goal of this is to prevent users from mistakenly using the development
website as if it were the real one.
Added dev website nginx configuration.
Restored the maintenance page + nginx config.

The maintenance mode is triggered with a file.
$ touch /var/www-prod/maintenance.mode # start maintenance
$ rm /var/www-prod/maintenance.mode    # end maintenance
Fixed parenthesis and repository update behavior.

Don’t update repository if we’re not about to commit. This allow to use
the script only to fetch translations.
#501 New page, only English and French for now.
#501 Added 13 translations
#499 Force timestamp on assets.
Add test case for problematic link merge of #504.
#424 #504 handle unique row bug without the moronic try/except, this also adds passing test cases for unique rows in the translations, favorites, and list tables
Merge branch 'dev' of https://github.com/Tatoeba/tatoeba2 into dev
Revert "Add test case for problematic link merge of #504."

This reverts commit 958232f3bf771d75ad44deab2e7bad8de5520a00.
Read unique constrained fields from model. #504
Comment on duplicate instead of merged sentence.

Closes #506.
#506 small optimization: add comments in one insert query
Make the dry option really dry.

Don’t even post comments or on the Wall.
Fix conflicting variable name. #504

This was obviously screwing up everything.
Improve link merging test case and fix self-links

Refs #504
Fix duplicates inside duplicates test case #504
Show percentage progress while deduplicating.