Use system proxy settings.

The resolver for 'identifiers.org' uses the Apache HTTP client, which by
default does not honor the JVM proxy settings. This commit updates the
resolver to force the client to use said settings.

closes #1231

protege-editor-owl/src/main/java/org/protege/editor/owl/model/identifiers/IdentifiersDotOrg.java

@@ -140,8 +140,6 @@ public List<IdoNamespace> getCollections() {
 
     @Nonnull
     private static HttpClient createClient() {
-        return HttpClientBuilder.create().build();
-
-
+        return HttpClientBuilder.create().useSystemProperties().build();
     }
 }