SCALEBAR aware of current scale

[Stephen Woodbridge]

It would be nice if the scalebar could be configured to with 
minscale/maxscale classes to you could configure it to change units like 
km -> m and mi -> ft when the scale gets smaller. Or better yet have an 
option for auto conversion of units.

It would also be nice if someone would add a scalebar that displays BOTH 
English and Metric over/under style like

0            0.5 mi        1 mi
|              |            |
+-----------+--+-----+------+
|           |        |
0        0.5 km     1 km


-Steve