added encoding within arguments in URL request, as it is required by Vizier ASU rules (further defined by RFC 1945)

introducing Request interface, Vizier request class, small refactor of VizierCataloguesWindow as it is possible to call Request's method

Introducing Data class as a superclass for Catalogue and Table.
Removing unnecessary FactoryCell class
Removing maximum output for catalogues via .meta-max=value as it is erroneous

slightly rewriting and refactoring MainWindowController. Now it is possible to hold data within separated windows (stages)