Export system data as a JSON file download

[alexander-harmaty]

Summary

• This feature adds a button to the edit and view pages that allows users to export their map data with a JSON file download
• It allows users to backup and preserve their data externally from MetroDreamin
• It also enables users to export their data for the use in other programs

Changes

• The creation of ImportAndExport.js, and ImportAndExport.scss to hold the functions and styling
• System.js imports the new component,
  • places the button within System-social.
  • passes the necessary properties to ExportSystemJSON
• default.scss imports the styling in ImportAndExport.scss
• Prompt.scss explicitly sets the font size for the confirm and deny buttons to resolve a sizing bug

How It Works

• ExportSystemJSON takes care of the main JSON export with helper functions orderProperties and formatJSON to improve JSON readability.
• ExportSystemJSON also contains handlers for a prompt to save when unsaved changes are present.

Issues Addressed

• Second request in #154
• Primary request in #220

Testing

• Tested the export functionality with and without unsaved changes to ensure the prompt and JSON behaved as expected
• Verified JSON objects match system data, including accurate geodata
• Confirmed JSON readability format consistency by testing with different cases of available data
  • different numbers of stations, interchanges, lineGroups, and lines, including zero
  • varying levels of detail in properties for stations and lines

Future Development

• Add a function named ExportSystemKML to support the KML format, addressing issue #173
• Add import functionality to support the two formats, addressing a follow-up request in issue #220
• Add specialized import and export functions to handle specific lines and stations instead of the whole system to address a use case to combine maps, detailed in issue #274