Pull updated translations from Transifex.
Add mn (Mongolian) language.
Do not update English translation for now as we want to keep
compatibility with 0.9.
Last update (48be9ce) missed quite a lot, for some reason.
This is also the first update done with the new script
`contrib/devtools/update-translations.py`
Update current translations, and add new languages:
- es_MX: Spanish (Mexico)
- pam: Kapampangan
Also update translation process for autoconf-based build system.
