[wizards] New options for groovy class creation

Should add 2 new options for Groovy class creation wizard:

• Create script check box (initially unchecked). Selecting this check box will initially create the groovy compilation unit as a script with no class declaration (but the package declaration will exist).
• File name text box. (Initially empty) Adding text here will change the file name of the groovy class, but not the default class. This allows a developer to (for example) create a file Foo.groovy, and have the class named Bar.