Implement ScaleStore

Thanks for the patch dwins. A few initial comments:

• Other stores that read data from OpenLayers objects have bind and unbind methods (see LayerStore and FeatureStore). If the store is constructed with an OL object, the constructor calls bind. This store could follow the same pattern. Alternatively, someone could not have the store bound to a map and could configure it with an array of scales.

• If the map does not have a base layer, this will not work. In this case, the bind method could register a listener for the "addlayer" event on the map. The listener should unregister itself when called. Unbind would also unregister the listener (in case it had not been called).

• See the other stores for examples of inline comments. We're sticking with NaturalDocs syntax for now.

• It would be good to keep adding to our examples by including one with each new class. You can crib from the existing examples.

attached patch addressing above concerns.

Looks great EXCEPT that the second test fails in IE6.

this last patch fixes the test in IE6.

(In [466]) A ScaleStore, which takes a map and provides records with information about zoom level, scale denominator, and map resolution. Thanks to dwins for the patch! (Closes #41)