Build .mo files automatically from buildout

Note: This uses c2c.recipe.msgfmt which seems to be unmaintained.
rm .mo files (fixes #738)
changelog entry
Use c2c.recipe.msgfmt from git to support symbolic links

See camptocamp/c2c.recipe.msgfmt#1.
Merge pull request #741 from xi/feature-738-rm-mo

rm .mo files