- External modifications to the db file can no longer be missed.

- Fixed dialogFinished signal of DatabaseOpenDialog was not emitted when dialog was closed via the 'X' (close) button

- For reloading with a modified db, an additional choice has been added to allow the user to ignore the changes in the file on disk.

- User is now presented with an unlock database dialog if reload fails to open the db automatically.
  For example when the user removed the YubiKey, failed to touch the YubiKey within the timeout period, or db pw has been changed.

Fixes keepassxreboot#5290

Mark db as modified when db file is gone or invalid.

…aloss