Fix #170: stray bar at bottom of /new page

#139 removed inline display:block from paste.html's created banner and
compensated with a global .created-banner { display:block } override.
That override also hit the hidden placeholder banner on /new, whose
base rule is display:none, making an empty padded bar render above the
action bar. Scope the override to .created-banner.show and mark only
the paste-view banner with the show class.

internal/web/templates/paste.html

@@ -35,7 +35,7 @@
   </div>
   {{if .JustCreated}}
   <div class="float">
-    <div class="created-banner">
+    <div class="created-banner show">
       Paste created. Link copied to clipboard: <a href="/{{.ID}}">{{.Host}}/{{.ID}}</a>
       {{if .DeletionToken}} · deletion token: <code>{{.DeletionToken}}</code>{{end}}
     </div>