Adapt French translation to the Transifex line endings

Since Transifex uses a slightly different convention for visual text formatting,
the French translation has been upload to Transifex and downloaded back to adapt
its formatting. The content was not changed, but subsequent diffs will be clearer.

Note that Tx breaks the file description header (with the name and copyright),
so it has to be restore manually each time before pushing to git.
Consequent update to the French translation

Most of the French translation has been proofread while playing the game,
thus leading to some improvements in terms of context and mood.
Some typos and language errors were fixed, and most strings should now follow
the common French typography rules.

Some strings were also edited to be more idiomatic, and also to comply with
my subjective sense of "what sounds good". That might be subject to debate :-)