Refactor Working Directory to OS-specific locations

[synthfi]

Changes

• getWorkingDirectory was split into: getConfigDirectory, getStateDirectory, and getTempDirectory
  • in each of the returned directories, a PolyGlot folder is created
  • The original functionality of unit tests using PolyGlot_TEST instead of PolyGlot is kept

Function	Linux Path	Windows Path	OSX Path
getConfigDirectory()	$XDG_CONFIG_HOME or ~/.config	%LOCALAPPDATA%	~/Library/Preferences
getStateDirectory()	$XDG_STATE_HOME or ~/.local/cache	%LOCALAPPDATA%	~/Library/Application Support
getTempDirectory()	$XDG_CACHE_HOME or ~/.local/state	%TEMP%	~/Library/Caches

• general refactors to use java.nio.file.Path instead of String & File
• updated tests
• getErrorLogFile can now throw IOException
• Unzipping of readme.zip is still done in a system temp directory as the designers of snap decided that snap packages should not be able to open files in hidden directories.
• Updated the About menu to list the locations of the config, state, and temp directories

Notes

• config is used for PolyGlot.ini. state is used for: autosave file, error log, webservice files (in sub-directory called WebServices). temp is used for: temp files (csv <-> excel), ...
• This brings understanding of the XDG base directory specification into PolyGlot. I tried my best to map these locations to windows & macos while keeping the source code simple. Please correct me if any of this is wrong.
• This is a stepping stone towards distribution as flatpak. This is the primary motivation behind this pr

Draft:

• [x] Add/update help menu to show what paths the app is using
• [x] update for creation of temp files for various things
• [ ] manually test excel file opening
• [ ] manually test font import file opening
• [ ] manually test logo import file opening
• [ ] manually test webservice file opening
• [ ] manually test print 2 pdf file opening
• [x] run tests on windows
• [x] run tests on macOS

Closes https://github.com/DraqueT/PolyGlot/issues/1349