Add a New "Extensions" Category

[andytudhope]

At Status, we have this cool concept called extensions. tl;dr they're a whole lot more fun than DApps. We want to curate them in this store too, using the same contract!

Steps

1. Add a new category, called "Extensions". We will need an image and colour for this from @errorists.
2. We will also need an "Extensions Profile" screen that displays a little info about what extensions are (in general) and what this particular extension will add to your Status experience (or how to get Status and use the extension if you're not browsing thru Status atm).
3. Add a new section below "Recently Added" on the home screen for "Extensions", with the same ranking components.
4. We can add extensions in the same way as we will add DApps, the URL will just be a bit more involved, so we shouldn't display that as we do for DApps.