Fixes to Starting window and Wallpaper windows.

- Checking for found wallpaper to match either mWallpaperTarget
or mLowerWallpaperTarget keeps from swapping the layers while
transitioning between two wallpaper activities.

- Fade out RecentsActivity while bringing up selected activity. This
keeps the RecentsActivity from showing through a launching wallpaper
activity.

- When moving a starting window from one activity to another clear
the startingDisplayed flag in the old activity.

- When moving a starting window from one activity to another assign
the new activity's mAppAnimator to the starting window's mWinAnimator.

- Only treat a wallpaper transition as entering if the mWallpaperTarget
is visible and not being hidden. Keeps from assigning the wrong
animation when activities are launched back to back and the
mWallpaperTarget is still animating away.

Fixes bug 7148089.

Change-Id: Idd405b1ba113f3345ca2116d141b474abe5bd4c0