Confirm with user before adding someone to twitlist

this seems like a good idea to prevent someone from accidentally blocking someone because of a misclick or because they didn't know what the icon did

webv4/components/twit-button.xjs

 <? var _bs = locale.get('button_block_sender', 'page_forum'); ?>
-<button id="bsb-%s" class="btn btn-default icon" aria-label="<? write(_bs); ?>" title="<? write(_bs); ?>" onclick="blockSender('%s', '%s', '%s')">
+<button id="bsb-%s" class="btn btn-default icon" aria-label="<? write(_bs); ?>" title="<? write(_bs); ?>" onclick="if (confirm('Permanently block this sender?')) { blockSender('%s', '%s', '%s') }">
     <span class="glyphicon glyphicon-ban-circle"></span>
 </button>
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