Manages a modal dialogue box that allows the user to define
projections using subclasses of ucar.unidata.gis.ProjectionImpl.
1) It uses bean introspection on ProjectionImpl subclasses to dynamically
configure edit fields for the projection's parameters. The subclass should
define getXXX() and setXXX() methods for each parameter.
2) A user-defined list of ProjectionImpl is maintained through a PersistentStore object.
3) when the user selects a projection, a NewProjectionEvent is sent to any listeners
4) currently the list of possible projection classes is maintained as a
hard-wired list of class names. This should be rethunk.