DiatactsActivity title indicate dialpad status, removed excessive "showing item"

messages.

+ DiatactsActivity set its' title to "Phone Dialpad" or just "Phone", so user
  using Talkback can know the state of the activity when it is launched
+ SpeedDialFragment and SearchFragment no longer send accessibility events when
  its' content is changed.
+ Add AccessibilityDelegate ContentChangedFilter to filter out
  TYPE_WINDOW_CONTENT_CHANGED event for View.

Bug:25190037
Change-Id: If1fa34cc9a5d24dec3fe261da9c071bb5388ec58