Move translation resources to a dedicated JavaScript source file

The translations are encoded in UTF-8, so most people in the world
can see it, but one may not be able to edit the file.  It's better
to separate them in a dedicated file for those people not interested
in translation.
Tweak parameters to enhance effect of mulching
Add ability to fertilize soil

Fertility of soil affects crops growth.  It grows naturally by wild
life activity, but you can boost it by fertilizing with cost of money.