feature: add package name to details sidebar

Author: edisile

templates/store/snap-details/_details.html

@@ -1,5 +1,11 @@
 <h2 class="u-off-screen">Details for {{ snap_title }}</h2>
 
+<h3 class="p-muted-heading">Package name</h3>
+<ul class="p-list">
+  <li>{{ package_name }}</li>
+</ul>
+<hr class="p-rule--muted">
+
 <h3 class="p-muted-heading">License</h3>
 <ul class="p-list">
   <li>{{ license }}</li>