Handle corrupted "user.config"

[unitycoder]

Had computer crash/BSOD, unitylauncherpro user.config file was corrupted and then application fails to launch.

info:
https://www.codeproject.com/Articles/30216/Handling-Corrupt-user-config-Settings
https://stackoverflow.com/questions/42708868/user-config-corruption

error:
System.Configuration.ConfigurationErrorsException: 'Configuration system failed to initialize'

[unitycoder]

restore backup can still fail, if backup file itself is broken..
need to save backup when it works and confirm that its xml file.

• validate backup file when creating it
• create secondary backup file?
• allow exporting settings to file (or basically, button to browse config folder, so user can take manual copy)
• dialog needs 3rd option, "reset settings", because if backup file is also broken, cannot get past this dialog, until go delete the file manually

[unitycoder]

added 3rd button for now