Add PLY extract generator for Catalyst

Does not include the ability to save out colors from the current
color array and transfer function.

Clients/ParaView/ParaViewExtractWriters.xml

 <ParaViewExtractWriters>
   <Category name="Data" show_in_toolbar="0" preserve_order="0">
+    <Proxy group="extract_writers" name="PLY" />
     <Proxy group="extract_writers" name="VTP" />
     <Proxy group="extract_writers" name="VTU" />
     <Proxy group="extract_writers" name="HTG" />

Remoting/Application/Resources/writers_ioxml.xml

@@ -1065,6 +1065,27 @@
   <!-- =================================================================== -->
   <ProxyGroup name="extract_writers">
 
+    <!-- ================================================================= -->
+    <DataExtractWriterProxy name="PLY">
+      <Documentation>
+        Extract writer to write polygonal data to the PLY file format.
+      </Documentation>
+      <StringVectorProperty name="FileName"
+                            number_of_elements="1"
+                            default_values="dataset_%.6ts.ply">
+        <Documentation>
+          Specify the filename to use.
+        </Documentation>
+      </StringVectorProperty>
+      <SubProxy>
+        <Proxy name="Writer" proxygroup="writers" proxyname="PPLYWriter" />
+        <ExposedProperties>
+          <Property name="Input" />
+          <Property name="FileType" />
+        </ExposedProperties>
+      </SubProxy>
+    </DataExtractWriterProxy>
+
     <!-- ================================================================= -->
     <DataExtractWriterProxy name="VTP">
       <Documentation>