refactoring initFxml method, adding executor shutdown after main stage is closed (i.e. application is closed)

data from MAST are now available in result window. Introducing /data folder for keeping data from catalogues
deleting k2_ffi, kepler_ffi and swift_uvot from MAST tables as they are not applicable

added error handling for Vizier part. Added "unlimited" parameter, so it won't limit user from downloading data with more than 50k rows.

Introducing Result Window with working table and columns showup. TODO: fill results with data

adding cds.savot parser, this is still in analytical phase as VOTable standards implemented in Vizier/Simbad/MAST differ

implemented retreiving GUI user data from Vizier, that includes Catalogues and its respective tables, constraints on selected columns.

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)