Add an option setting the direction of switching workspace

[demokritos]

Workspace-to-dock extension allows the workspaces to lay in horizontal direction. If workspaces are in horizontal direction, switching workspace by scrolling on the dock does not work. This PR adds a checkbox for horizontal workspace switching in the preference and a switcher popup source code from the Workspace-to-dock extension.

[micheleg]

Hi,

thanks for your contribution. I had a look at the code and everything seems to make sense. However, I'm a bit puzzle about the inclusion of such feature. I'm wondering if there's a way for workspace-to-dock to be more compatible without requiring change in other extensions.

I'll have to think a bit about it.

[passingthru67]

@demokritos, I probably should have made the workspaces-to-dock horizontal switching an alternative instead of the default. Anyway, I can add an option that will give users a choice.

[demokritos]

OK.
Thanks for your time.