Let Windows create memory dump on program crash

[hugbug]

When NZBGet crashes it attempts to write call stack into log-file. For that purpose it installs an exception handler. After doing its job the handler terminates the program. It does it in a way preventing Windows from creating memory dump. However such memory dumps can be useful for debugging.

In this issue:

• rework exception handler to let Windows writing memory dumps, after the call stack is logged.
• provide an option to disable writing of call stack traces. The exception handler (required to write call stack trace) brings the program into a state which is different from the state when the crash occurred. The created memory dumps become less useful.