Doc translations are outdated

While there has been a big effort in providing initial translations, we are lacking maintainers for individual translations which means that the translated pages are very quickly outdated with respect to the original english versions.

Providing out of date or incorrect translated documents is in my opinion worse than not providing any translation at all, but that is an arguable opinion. However, there are some parts of the translated sites that are blatantly outdated and are causing a lot of **harm** to the mapserver project as a whole: I was pointed this morning to the french translation of the download page that stated that our **last release was 5.6.1 from more than 3 years ago** !

I do not have a canned solution for this problem, but something **must** be done to address these issues. Possible solutions include:
- removing a translation if it is not being actively maintained.
- overriding a translated page by it's original english version if the last commit date of the translated page is older than the english page.
- printing a message warning on the top of the pages where the last commit date of the translated page is older than the english page.