Always put checkbox labels on the right (#2937)

There were two checkboxes with labels set on the left: it was looking
weird and inconsistent with the rest of the application.

Also, since the Websub checkbox cannot be checked by the user (i.e. it
is entirely managed by the backend), I just hide the line when Websub is
disabled. It would be better to never show the checkbox and adapt the
label to say something like "Websub is enabled for this feed", but I
prefer to avoid changing all the locales.

Last point: an input should always have one and only one label. Websub
checkbox had two labels, which can be hardly supported by assistive
technologies.

Reference: https://developer.mozilla.org/en-US/docs/Learn/Forms/How_to_structure_a_web_form#Multiple_labels

app/views/helpers/feed/update.phtml

@@ -232,14 +232,18 @@
 				</label>
 			</div>
 		</div>
-		<div class="form-group">
-			<label class="group-name" for="pubsubhubbub"><?= _t('sub.feed.websub') ?></label>
-			<div class="group-controls">
-				<label class="checkbox" for="pubsubhubbub">
-					<input type="checkbox" name="pubsubhubbub" id="pubsubhubbub" disabled="disabled" value="1"<?= $this->feed->pubSubHubbubEnabled() ? ' checked="checked"' : '' ?> />
-				</label>
+
+		<?php if ($this->feed->pubSubHubbubEnabled()) { ?>
+			<div class="form-group">
+				<div class="group-controls">
+					<label class="checkbox" for="pubsubhubbub">
+						<input type="checkbox" name="pubsubhubbub" id="pubsubhubbub" disabled="disabled" value="1" checked />
+						<?= _t('sub.feed.websub') ?>
+					</label>
+				</div>
 			</div>
-		</div>
+		<?php } ?>
+
 		<div class="form-group form-actions">
 			<div class="group-controls">
 				<button class="btn btn-important"><?= _t('gen.action.submit') ?></button>
@@ -310,9 +314,11 @@
 		</div>
 
 		<div class="form-group">
-			<label class="group-name" for="clear_cache"><?= _t('sub.feed.clear_cache') ?></label>
 			<div class="group-controls">
-				<input type="checkbox" name="clear_cache" id="clear_cache" value="1"<?= $this->feed->attributes('clear_cache') ? ' checked="checked"' : '' ?> />
+				<label class="checkbox" for="clear_cache">
+					<input type="checkbox" name="clear_cache" id="clear_cache" value="1"<?= $this->feed->attributes('clear_cache') ? ' checked="checked"' : '' ?> />
+					<?= _t('sub.feed.clear_cache') ?>
+				</label>
 			</div>
 		</div>