When data is added to the circular, first check if it is already
present. In that case, the item is moved to the beginning of the
circular clipboard.

This avoids dropping old data prematurly, and traversing the same data
multiple times when pasting.

Change-Id: Iecaf8d2f5a05d08e6f5faa8555d24f4d7a1d33ab
Reviewed-by: Leandro Melo <leandro.melo@nokia.com>