Re-enable snippets

Fixed colors to use the same as refactoring rename, and a few
fixes for undo and document changes outside the tab areas.

Reviewed-by: Roberto Raggi

src/plugins/texteditor/basetexteditor.h

@@ -380,7 +380,7 @@ public:
 
     void setTextCursor(const QTextCursor &cursor);
 
-    void insertCodeSnippet(const QString &snippet);
+    void insertCodeSnippet(const QTextCursor &cursor, const QString &snippet);
 
 public slots:
     void setDisplayName(const QString &title);