Fixed issues and enhanced the workspace caption popup menu.

Details:
Moved window count code from thumbnailsBox to workspaceThumbnail class
Changed popup menu source actor to caption background
Fixed issue where dock hid when popup menu opened over maximized window
Fixed issue where window app button stayed large
Modified popup menu window apps list to include a close button
Added custom classes for the popup menu window apps list
thumbnailsBox - code cleanup.
Changed caption popup menu window-close icon from symbolic to GS themed.
Fixed GS34 issue where GS classes cannot be overridden so menu window-close icon cannot be resized. Use custom class alone in GS34.