Add scythe tool and wheat seeds

[zorfmorf]

There are some special wheat tiles with growing grass. Can only be harvested with a scythe (but several tiles at once!)

[zorfmorf]

Scythe is already added, need to add the correspondig seeds first

[zorfmorf]

When a wheat tile updates itself, it needs to check if it is surrounded by wheat plants in a similar state. Sheesh. The plant update routine therefore needs to do the following

• Update all plants (they update their state)
• Update all wheat plant visuals (additional method)

Then we can do the wheat plant logic "if left is a same wheat but not right or above use texture x". Ugh

[zorfmorf]

Done. Some special case texture issues left, but the feature in itself is done and not feeling like tackling that immediately