slapos_pdm: add missing strict parameter and implementation

   Strict returns directly a single Software Release for a giving url.

master/bt5/slapos_pdm/SkinTemplateItem/portal_skins/slapos_pdm/SoftwareProduct_getSortedSoftwareReleaseList.py

@@ -15,6 +15,9 @@ if software_product_reference is None:
   if not software_release:
     return []
   
+  if strict:
+    return [software_release]
+
   software_product_reference = software_release.getAggregateReference()
   if not software_product_reference:
     return []

master/bt5/slapos_pdm/SkinTemplateItem/portal_skins/slapos_pdm/SoftwareProduct_getSortedSoftwareReleaseList.xml

@@ -50,7 +50,7 @@
         </item>
         <item>
             <key> <string>_params</string> </key>
-            <value> <string>software_product_reference=None, software_release_url=None</string> </value>
+            <value> <string>software_product_reference=None, software_release_url=None, strict=None</string> </value>
         </item>
         <item>
             <key> <string>id</string> </key>