Make PluginManager mostly static.

Change-Id: Ib938aa4999c7c418a82304c5cca2e8748ef9d228
Reviewed-by: hjk <qthjk@ovi.com>

src/plugins/coreplugin/outputpanemanager.cpp

@@ -247,8 +247,7 @@ void OutputPaneManager::init()
     QFontMetrics titleFm = m_titleLabel->fontMetrics();
     int minTitleWidth = 0;
 
-    m_panes = ExtensionSystem::PluginManager::instance()
-        ->getObjects<IOutputPane>();
+    m_panes = ExtensionSystem::PluginManager::getObjects<IOutputPane>();
     qSort(m_panes.begin(), m_panes.end(), &comparePanes);
     const int n = m_panes.size();