Android TV leanback banner

Adds an Android TV leanback banner to Briar.

Just put this together so it'll be easier to test Briar on Android TV without needing Sideload Launcher.

I've also provided an SVG version of the banner, just in case.

I wouldn't suggest publishing for Android TV just yet though as there are a lot of interface issues (you can still publish this APK to Google Play, you'd just have to disable Android TV support in the Google Play developer console).

It's very difficult to get the cursor to highlight certain elements and buttons, and it's difficult to tell if they are highlighted or not, some buttons can't be hit at all and the on-screen keyboard often doesn't work for chatting (you have to use an external keyboard or the phone app to type messages.

Also something to mention, Briar as it is on Google Play right now likely supports the LG Google TV devices that run Android 4.2.2, they're extremely rare [as they've been discontinued and Google TV wasn't popular] and they're the only Google TV devices that got updated past version 3.2, so it's minor but still interesting to me.