core: contest: support realtime scoreboard after freeze contest (#544)

Co-authored-by: panda <panda_dtdyy@outlook.com>

packages/ui-default/templates/contest_edit.html

@@ -165,7 +165,7 @@
               name:'lock',
               placeholder:_('(leave blank if none)'),
               value:(((tdoc.endAt - tdoc.lockAt)/60000)|int) if tdoc.lockAt else '',
-              help_text:_('Lock scoreboard on last N minutes'),
+              help_text:_('Freeze scoreboard with N minutes remaining'),
               disabled:true,
               row:false
             }) }}