multiCursorModifier should be ctrlCmd by default for *nix users

- VSCode Version: Code - Insiders 1.15.0-insider (6328bae2bf8382fd4abd054c14976548eaea66cf, 2017-07-27T07:00:51.592Z) - OS Version: Linux x64 4.10.0-28-generic - Extensions: none --- Following on the heels of #21506, I feel that the default click action for *nix users should not be alt-click, but ctrl-click. What's odd is I only see references to ctrl-click in the issue, but somehow...  Alt-click is mapped by default in Ubuntu window manager to move windows, so alt-click in this case does nothing (or rather, it moves the vscode window) Perhaps this is more a question than a bug, but: 1. Is this configurable in `settings.json`, so it is ctrl-click? 2. If not, can the default be changed to ctrl-click so it functions on Ubuntu at least?