Add summary stats plugin in html.

librestash/templates/stats/plugins/summary.html

+<table>
+ <tr>
+  <td>Total Finds</td>
+  <td>{{ data['totals']['found'] }} found logs</td>
+ </tr>
+
+ <tr>
+  <td>Cache Types</td>
+  <td>{{ data['totals']['types'] }} different types found</td>
+ </tr>
+
+ <tr>
+  <td>Cache Sizess</td>
+  <td>{{ data['totals']['sizes'] }} different sizes found</td>
+ </tr>
+
+ <tr>
+  <td>Difficulty</td>
+  <td>
+   Minimum: {{ data['min_max_avg']['difficulty'][0] }}
+   Maximum: {{ data['min_max_avg']['difficulty'][1] }}
+   Mean (harmonic): {{ data['min_max_avg']['difficulty'][2] }}
+  </td>
+ </tr>
+
+ <tr>
+  <td>Terrain</td>
+  <td>
+   Minimum: {{ data['min_max_avg']['terrain'][0] }}
+   Maximum: {{ data['min_max_avg']['terrain'][1] }}
+   Mean (harmonic): {{ data['min_max_avg']['terrain'][2] }}
+  </td>
+ </tr>
+</table>