[TP] Preview click opens wallpaper selector [2/3].

Adds click handling to the preview section which opens the full-screen
wallpaper chooser experience.

Fix: 268562476
Test: manually verified that clicking on the preview on the main page
opens the wallpaper screen
Test: manually verified this for home screen tab
Test: manually verified this for lock screen tab
Test: manually verified that, on the lock screen tab, clicking works as
described above, on, or below the clock carousel and that the clock
carousel still handles left/right gestures to change clocks

Change-Id: I8a819730a03992b190830010ddc022eae7e09b30