banner: Allow label to be in HTML format.

This is done to later render the subscribe
success and error messages using the banner
template instead of using the banner classes
in the subscription/memebership templates
which requries us to duplicate the changes
in banner.hbs at these places to avoid
regressions.

Signed-off-by: apoorvapendse <apoorvavpendse@gmail.com>

web/templates/components/banner.hbs

@@ -1,7 +1,11 @@
 <div {{#if process}}data-process="{{process}}"{{/if}} class="{{#if custom_classes}}{{custom_classes}} {{/if}}banner banner-{{intent}}">
     <span class="banner-content">
         <span class="banner-label">
-            {{label}}
+            {{#if label}}
+                {{label}}
+            {{else}}
+                {{> @partial-block .}}
+            {{/if}}
         </span>
         <span class="banner-action-buttons">
             {{#each buttons}}