Merge CppTools into CppEditor

There was no proper separation of responsibilities between these
plugins. In particular, CppTools had lots of editor-related
functionality, so it's not clear why it was separated out in the first
place.
In fact, for a lot of code, it seemed quite arbitrary where it was put
(just one example: switchHeaderSource() was in CppTools, wheras
switchDeclarationDefinition() was in CppEditor).
Merging the plugins will enable us to get rid of various convoluted
pseudo-abstractions that were only introduced to keep up the artificial
separation.

Change-Id: Iafc3bce625b4794f6d4aa03df6cddc7f2d26716a
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/clangcodemodel/clangoverviewmodel.h

@@ -27,7 +27,7 @@
 
 #include "tokeninfocontainer.h"
 
-#include <cpptools/abstractoverviewmodel.h>
+#include <cppeditor/abstractoverviewmodel.h>
 
 namespace ClangBackEnd { class TokenInfoContainer; }
 
@@ -51,7 +51,7 @@ public:
     const ClangBackEnd::TokenInfoContainer token;
 };
 
-class OverviewModel : public CppTools::AbstractOverviewModel
+class OverviewModel : public CppEditor::AbstractOverviewModel
 {
     Q_OBJECT