Add ConnectionConfiguration.setProxyInfo(ProxyInfo)

Fixes SMACK-661.

smack-core/src/main/java/org/jivesoftware/smack/ConnectionConfiguration.java

@@ -614,6 +614,17 @@ public abstract class ConnectionConfiguration {
             return getThis();
         }
 
+        /**
+         * Set the information about the Proxy used for the connection.
+         *
+         * @param proxyInfo the Proxy information.
+         * @return a reference to this builder.
+         */
+        public B setProxyInfo(ProxyInfo proxyInfo) {
+            this.proxy = proxyInfo;
+            return getThis();
+        }
+
         /**
          * Allow <code>null</code> or the empty String as username.
          *