Can not mark the same content of browser page after copy

Marking a text on the web page and then press copy works,
but trying to mark the same text again does not work.
The reason for this is that the selection never gets
cleared in webkit.
The fix, calling cleaSelection in the onDestroyActionMode.
Also added clearSelection when getting an
onConfigurationChange.

Change-Id: I59b384cb5441b6a3a05007ea7e77f9699889a87c