QmlDesigner: Replace custom +/- button icons in connectioneditor

Use the themable ones from Core::Icons instead

Change-Id: I45e831e9b0586bfde6468acca07b6138b48f82e0
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@theqtcompany.com>

src/plugins/qmldesigner/qmldesignerextension/connectioneditor/connectioneditor.qrc

 <RCC>
     <qresource prefix="/connectionview">
         <file>stylesheet.css</file>
-        <file>plus.png</file>
-        <file>minus.png</file>
     </qresource>
 </RCC>

src/plugins/qmldesigner/qmldesignerextension/connectioneditor/connectionviewwidget.cpp

@@ -33,6 +33,7 @@
 #include "dynamicpropertiesmodel.h"
 
 #include <coreplugin/coreconstants.h>
+#include <coreplugin/coreicons.h>
 #include <utils/fileutils.h>
 
 #include <QToolButton>
@@ -118,13 +119,13 @@ QList<QToolButton *> ConnectionViewWidget::createToolBarWidgets()
     QList<QToolButton *> buttons;
 
     buttons << new QToolButton();
-    buttons.last()->setIcon(QIcon(QStringLiteral(":/connectionview/plus.png")));
+    buttons.last()->setIcon(Core::Icons::PLUS.icon());
     buttons.last()->setToolTip(tr("Add binding or connection."));
     connect(buttons.last(), SIGNAL(clicked()), this, SLOT(addButtonClicked()));
     connect(this, SIGNAL(setEnabledAddButton(bool)), buttons.last(), SLOT(setEnabled(bool)));
 
     buttons << new QToolButton();
-    buttons.last()->setIcon(QIcon(QStringLiteral(":/connectionview/minus.png")));
+    buttons.last()->setIcon(Core::Icons::MINUS.icon());
     buttons.last()->setToolTip(tr("Remove selected binding or connection."));
     buttons.last()->setShortcut(QKeySequence(Qt::Key_Delete));
     connect(buttons.last(), SIGNAL(clicked()), this, SLOT(removeButtonClicked()));

src/plugins/qmldesigner/qmldesignerplugin.qbs

@@ -583,8 +583,6 @@ Project {
                 "connectioneditor/connectionviewwidget.ui",
                 "connectioneditor/dynamicpropertiesmodel.cpp",
                 "connectioneditor/dynamicpropertiesmodel.h",
-                "connectioneditor/minus.png",
-                "connectioneditor/plus.png",
                 "connectioneditor/stylesheet.css",
                 "pathtool/controlpoint.cpp",
                 "pathtool/controlpoint.h",