Improvements for Android TV (#17524)

* Improvements for Android TV

To build for Android TV, user need to modify the orientation from "portrait" to "landscape"
for the four activities in tensorflow/examples/android/AndroidManifest.xml

1. Show a toast when no camera is detected
2. Game Controller L1 button and remote controller DRAP_Center also triggers debug output
3. Fix the layout of Stylize app on Android TV. The style selector will be on right side
4. User can use DPAD to navigate through styles in Stylize app

* Fix README grammar, keyDown pass down, and unused import

* Calculate style selector width and num of style in a row programmatically

* Fix imports