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.cpp

@@ -218,16 +218,17 @@ void VcsBaseEditorParameterWidget::mapSetting(QComboBox *comboBox, int *setting)
     comboBox->blockSignals(false);
 }
 
-void VcsBaseEditorParameterWidget::executeCommand()
-{
-}
-
 void VcsBaseEditorParameterWidget::handleArgumentsChanged()
 {
     updateMappedSettings();
     executeCommand();
 }
 
+void VcsBaseEditorParameterWidget::executeCommand()
+{
+    emit commandExecutionRequested();
+}
+
 VcsBaseEditorParameterWidget::OptionMapping::OptionMapping() :
     widget(0)
 {