qt: Show also value for options overridden on command line

Currently only the name of the option is shown for GUI options
overridden by command line (or configuration file). This commit
adds the value of the options as well, which is useful for
troubleshooting.
Merge pull request #3867

b40bdd6 qt: Show also value for options overridden on command line (Wladimir J. van der Laan)