Bug 1026257 - Would like to be able to set default number of columns in ...

...vertical homescreen at build time
Hmm, I was a bit hesitant at adding the verticalPreferences object in the gaia-grid as it has no place in collections or search app. I really don't think that we should add the configurator here, it really defeats the purpose of having a reusable component. The configurator is not present in the collection or search app for example.

I think the proper fix here is probably having the vertical homescreen make the configuration call, then set grid.setAttribute('cols', 3 || 4). What do you think?