DeskClock: fix crash when trying to view world cities

Add proguard.flags and keep class android.support.v7.widget.SearchView

fixes:
SupportMenuInflater: Cannot instantiate class: android.support.v7.widget.SearchView
SupportMenuInflater: java.lang.NoSuchMethodException: <init> [class android.content.Context]
AndroidRuntime: java.lang.NullPointerException:
Attempt to invoke virtual method 'void android.support.v7.widget.SearchView.setImeOptions(int)' on a null object reference

Change-Id: Iaa260193d48ac086cf54232b433b9dcf7b8ba361