ui: add problem_search snippet for homepage

packages/ui-default/templates/partials/homepage/problem_search.html

@@ -0,0 +1,13 @@
+<div class="section side">
+  <div class="section__header">
+    <h1 class="section__title">{{ _('Search') }}</h1>
+  </div>
+  <form method="get" action="p">
+    <div class="section__body">
+      <label>
+        <input name="q" type="text" class="textbox" value="" placeholder="1001">
+      </label>
+      <button type="submit" class="primary button">{{ _('Search') }}</button>
+    </div>
+  </form>
+</div>