Vcs: in VcsBaseClient use functors to create log/diff parameter widgets

Also API of VcsBaseEditorParameterWidget was changed to take benefit of C++11 lambdas.
Slot executeCommand() is no longer virtual and only fires signal commandExecutionRequested().
The Vcs client just has to bind a lambda to this signal instead of some boiler-plate code
like keeping track of the arguments of diff/log with "struct XxxDiffParameters", etc.

Change-Id: I347c97d84a8324e9c661df4e6d9a6075980b020f
Reviewed-by: Tobias Hunger <tobias.hunger@theqtcompany.com>

src/plugins/vcsbase/vcsbaseeditorparameterwidget.h

@@ -80,10 +80,12 @@ public:
     virtual QStringList arguments() const;
 
 public slots:
-    virtual void executeCommand();
-    virtual void handleArgumentsChanged();
+    void handleArgumentsChanged();
+    void executeCommand();
 
 signals:
+    void commandExecutionRequested();
+
     // Trigger a re-run to show changed output according to new argument list.
     void argumentsChanged();