Add an "add person" icon

[eamodio]

Something like this:

I would like to use it in GitLens for adding co-authors. The above is the icon I am currently using, but the plus should probably be an overlay in the bottom right like our other + icons.

[miguelsolorio]

Since this icon is a bit smaller compared to other icons (new folder/file), I used the smaller plus that's also used in our emoji icon: