Better resource handling in TestAndReset + beep/blink startup.

Replaces raw pointer with std::unique_ptr to prevent potential
resource leak.

Add an option to make the beep/blink on module startup configurable.
This closes #51.
Rpleth card_convert_from_text refactoring.

* This method is now static, as it greatly improves testability.
* Replace an assert() by a proper return value.