provide an option to export/import configuration and allow specifying used one via command line

[GitMensch]

Better idea: provide an option to select to configuration via command line. That would take care of all the other stuff (sysroot, ...) too

Originally posted by @lievenhey in #556 (comment)

I extend the suggested option by an export/import (or save/load) option in the settings dialog, as I have no clue where the configuration should come from. If I understood this part wrong, then feel free to drop that part.

For the command line: any explicit set option should override/extend the given configuration file. If that's not easily possible it would be order precedence [so everything is reset if --configuration is parsed which may should be left as hint in the help text].

[lievenhey]

You can use this setting in the config dialog to save the settings in a "preset". My idea was that you can also load this "preset" from the command line.