Improve the device selector on doc.e.foundation

UI problems

We mention Smartphones and Laptops in the header at doc.e.foundation, but not tablets. This is misleading. It implicitly says we don't support tablets. If we are not ok to add a 3rd menu item for Tablets, then let's combine all under devices.

Proposal

Combine all categories in one Devices
Improve the filter selector and make Smartphone, Tablet, Laptop or All more obvious

I'd recommend we elevate the device type selector with the following entries: Laptop, Smartphone, Tablet, All. We probably want this to be visible for all.

We also probably want to highlight the type of release Stable, Community, Test and how you can install it: Easy Installer, Command line. We should add some context about the terms, too.

Then we can show the brand, model selector on demand.

Example

Quick proposal to get the discussion started

@rhandros @rhunault @manojnair