Added hint with default value to the conference server line editor

resources/preferences.ui

@@ -879,7 +879,14 @@
              </widget>
             </item>
             <item row="16" column="1" colspan="5">
-             <widget class="QLineEdit" name="conference_server_editor"/>
+             <widget class="LineEdit" name="conference_server_editor">
+              <property name="widgetSpacing" stdset="0">
+               <number>0</number>
+              </property>
+              <property name="inactiveText" stdset="0">
+               <string>conference.sip2sip.info</string>
+              </property>
+             </widget>
             </item>
            </layout>
           </widget>