Temporarily use PNG icons over SVG

Issue #122:
SVG image reader is a plugin (not part of QtCore/QtGUI).
It needs to be included in the package of any application that needs to read SVG images.
Until this happens, we use the PNG version of the icons.

Libs/Widgets/Plugins/ctkSearchBoxPlugin.cpp

@@ -47,7 +47,7 @@ QString ctkSearchBoxPlugin::domXml() const
 // --------------------------------------------------------------------------
 QIcon ctkSearchBoxPlugin::icon() const
 {
-  return QIcon(":/Icons/search.svg");
+  return QIcon(":/Icons/search.png");
 }
 
 //-----------------------------------------------------------------------------

Libs/Widgets/Resources/ctkWidgets.qrc

@@ -6,6 +6,8 @@
     <file>Icons/expand-down.png</file>
     <file>Icons/expand-up.png</file>
     <file>Icons/search.svg</file>
+    <file>Icons/search.png</file>
     <file>Icons/clear.svg</file>
+    <file>Icons/clear.png</file>
   </qresource>
 </RCC>

Libs/Widgets/ctkMenuComboBox.cpp

@@ -89,7 +89,7 @@ void ctkMenuComboBoxPrivate::init()
 
   // SearchButton
   this->SearchButton = new QToolButton();
-  this->SearchButton->setIcon(QIcon(":/Icons/search.svg"));
+  this->SearchButton->setIcon(QIcon(":/Icons/search.png"));
   this->SearchButton->setCheckable(true);
   this->SearchButton->setAutoRaise(true);
   this->SearchButton->setSizePolicy(QSizePolicy::Fixed,QSizePolicy::Ignored);

Libs/Widgets/ctkSearchBox.cpp

@@ -61,8 +61,8 @@ public:
 ctkSearchBoxPrivate::ctkSearchBoxPrivate(ctkSearchBox &object)
   : q_ptr(&object)
 {
-  this->clearIcon = QIcon(":Icons/clear.svg");
-  this->searchIcon = QIcon(":Icons/search.svg");
+  this->clearIcon = QIcon(":Icons/clear.png");
+  this->searchIcon = QIcon(":Icons/search.png");
   this->clearIconMode = QIcon::Disabled;
   this->showSearchIcon = false;
   this->alwaysShowClearIcon = false;