Seeding make corns to grow

The vegetables are only showing up, you cannot harvest them yet.
Add corn growth readout to status window
Add working power showing window at bottom right of the screen

The player costs working power when doing some task such as cultivating
or seeding.  Cultivating is relatively hard physical work, taking much
working power.
Add select mode that does nothing when clicked

The select mode have no purpose in a PC, but it's useful in touch panel
UI devices since the user have no means to just select and see
information of a random cell without it.

It's also a safe mode to prevent accidentally wasting working power to
cultivating or something.
Add serialize methods, save/load, autosave and reset button features

They are rich set of features that could be separated into smaller
commits, but they are deeply related together that forcing subdivision
of commits are somewhat painful.

They are also proven feasible by turrets project, so we do not need
fine granularity for the sake of debugging.
Fix cultivated ridges do not appear when loaded from serialized stream