OpenDingux: Make the exit code 1 when fatal errors occur during initialisation.
OpenDingux gui.c: Prevent a cppcheck warning regarding use of an uninitialised variable.
OpenDingux: Dramatically simplify the drawing of centered and right- or bottom-aligned text.
OpenDingux: Add confirmations for overwriting and deleting saved states. Add screens for basic initialisation errors and file access errors.