Bug 1029902 - [Vertical Homescreen] Implement device capability configuration

The following changes are made for low capability devices:

* Icons default to 4 per row.
* Icon resolution is reduced.
* Icon rendering does not account for devicePixelRatio.

https://bugzilla.mozilla.org/show_bug.cgi?id=1029902
Just an idea that you can omit.

const CAPABILITIES = {
   LOW: 'low',
   HIGH: 'high' <- I don't know if this value exists :)
}