Economy health chart

Currently the game statistic informs you over your production, but not what is consumed by your economy. This information can be helpful to rate your current economic situation.

As a bare consumption chart will only have a limited use a chart, which display the difference between production and consumption should be implemented.
For now I call it the Economic Health Chart, but I'm still searching for a good name ;)

The discussion about this feature can be found at:
http://wl.widelands.org/forum/topic/878/