2.3.x scale hint

This PR solves the http://jira.codehaus.org/browse/GEOS-572

The ScaleHint element was added in the capabilities service for WMS 1.1.1. On the other hand,  the MinScaleDenominator and MaxScaleDenominator elements were included in the capabilities servicies for WMS 1.3.0.

This approach takes the minimum and maximum scale values from the set of style's rules containted in the layer information. By default, the MinScaleDenominator = 0.0 and MaxScaleDenominator  = infinity.