Add Menu Dropdowns

[crugas]

Issue:
Add a menu dropdown with the following features:

• File
  • Clear output file - delete all files in the output folder
  • Edit ASpace Login - allow user to change their ArchivesSpace login credentials from within the main app
  • Reset Defaults - reset user default settings
  • Exit
• Help
  • User Manual - link to the GitHub Wiki User Manual page (need to construct this)
  • About - show app version and ability to check for update (link to GitHub releases page) and check GUI info (using sg.popup_scrolled(sg.get_versions(), non_blocking=True, keep_on_top=True))

Resolution:
Add feature as listed above

Issue tracker:

• Looked through the User Manual and found no solutions
• Found no closed or open issues on the Issues page
• Have downloaded and running the latest version of the program