Add default error types

[Jeehut]

Probably useful error types:

• MungoError(message: String): A BaseError with a custom message.
• MungoFatalError(message: String) A FatalError with a custom message.
• MungoHealableError(message: String, healTitle: String, healHandler: () -> Void): A HealableError with a Cancel and a healing button.