idea taken from homedecor_modpack and its homedecor_i18n
all translated mods have a new dependency : plantlife_i18n
translations are stored in po/pot file : one file for all mods
added french translation (almost complete)
transfered de/es/tr/pt translations to corresponding .po file
(only for some mods, unfortunately translations are incomplete)
Because minetest.after() is not bound to a position, and because it is not
saved, it may trigger after the node to which it applies was unloaded, or
not at all (if the session ends). If that happens, The 'young' flag
will not be cleared, and will have become persistent (i.e. without a timer
which will eventually clear it).
This patch removes the 'young' flag, and replaces it with a timestamp, removing
the need for a timer. Any lingering 'young' flags that have become persistent
are automatically removed over time (i.e.: they are simply ignored...)
