Plugin config for portable mode

[Hirogen]

further changes to portable mode!
portableMode configuration and plugin configuration is now saved in a subfolder "portable" in the application startup directory, this should help with separation of files.

• portableMode.json can just be moved to the new folder
• plugin configuration files, currently saved in %appdata%\logexpert, can be copied to applicationstartuppath/portable/ and are loaded from this location in portableMode
• sessionFiles in portable mode are saved in the "sessionfiles" folder in the application startup folder, again for file separation and organisation

this should now fix #233 and logexpert should now have a full portable mode, where all configuration and session data is saved in the application startup directory