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.
qt: Enable and disable the Show and Remove buttons for requested payments history
based on whether any entry is selected.
Merge pull request #3874

caee92d qt: Enable and disable the Show and Remove buttons for requested payments history based on whether any entry is selected. (Haakon Nilsen)
Merge pull request #3867

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