Add a clone view for presenter.

The cloned editor is displayed in another window, and synchronized with the current editor.
Available in Window->Clone Editor.
(cherry picked from commit 2fba9ba1809a5ddfe44cbe807e9a1566f014ecf6)

Conflicts:
	src/plugins/coreplugin/coreconstants.h
	src/plugins/coreplugin/editormanager/editormanager.cpp