Show Change Tracking toolbar, prepare hiding/positioning:

Show Change Tracking toolbar, prepare hiding/positioning:

 - src/frontends/Toolbars.h: control displaying of CT toolbar with a parameter
 - src/frontends/Toolbars.C: control displaying of CT toolbar with a parameter
 - src/frontends/LyXView.C : show CT toolbar
 - src/ToolbarBackend.C    : add CT toolbar to default.ui as REVIEW
 - lib/ui/default.ui       : add CT toolbar to default.ui
 - src/ToolbarBackend.h	   : add CT toolbar type  REVIEW

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@15598 a592a061-630c-0410-9148-cb99ea01b6c8