Macros: Modernize

* Replace 0 with nullptr
* Remove redundant pimpl
* Use inline member initialization

Started-by: Laurent Montel <laurent.montel@kdab.com>
Change-Id: I15ace2581c13ecf24b7c947972b9435fbcaa12ab
Reviewed-by: Laurent Montel <laurent.montel@kdab.com>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/macros/macrosplugin.cpp

@@ -48,10 +48,6 @@
 
 using namespace Macros::Internal;
 
-MacrosPlugin::MacrosPlugin() : m_macroManager(0)
-{
-}
-
 MacrosPlugin::~MacrosPlugin()
 {
     delete m_macroManager;