reimplemented of how the application retrieves and stores data

See merge request !2

refactored the way of how application gets data from servers and how it stores them in application. The application does not save the data into files anymore, instead it keeps them in memory and uses them as soon as possible.

refactored so that now application stores data in string instead of saving it into the file (applies now to catalogue meta data as well)

refactored retrieving data. now the application returns the string instead of saving the result into file

adding input, radius, radiustype into JSON export structure, introducing OutputData such as the structure to represent values that should be exported

Refactored to Spring Boot

See merge request !1

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.