Base class for Pivot themes. A theme defines a complete "look and feel" for a Pivot application.
Note that concrete Theme implementations should be declared as final. If multiple third-party libraries attempted to extend a theme, it would cause a conflict, as only one could be used in any given application.
IMPORTANT All skin mappings must be added to the map, even non-static inner classes. Otherwise, the component's base class will attempt to install its own skin, which will result in the addition of duplicate listeners.