Fix search bar UI in All Apps

Commit Ifa9fabe3a8236513fad8030c0bd8ed4d27ebd549 improved the look
of the search bar, however it had a few issues and the overall
look did not match Settings or Widget search style.

The following improvements have been made:
 - Centered the search bar text vertically inside the search bar
 - Fixed poor contrast of the search bar text against the background
 - Added back search icon that is always shown, matching Widget search
 - Changed paddings to match Widget search

Change-Id: Ia127da05adff45f8860f0870817aaa9fde8e171c