Add manual refresh control to map.

It may or may not be permanenet, once tasks #322, #323, #324, #325
are implemented.

Closes #326

lib/www/client/source/src/views/Map.vue

@@ -190,6 +190,18 @@
           :indeterminate="loadingProgress === null"
           :value="loadingProgress"
         >{{ Math.round(loadingProgress) }}%</v-progress-circular>
+        <div v-else>
+          <v-icon
+            class="my-1"
+            title="Manual refresh"
+            @click="refresh"
+            >mdi-cloud-refresh-variant-outline</v-icon>
+        </div>
+      </div>
+    </div>
+
+    <div class="map-overlay bottom left">
+      <div>
       </div>
     </div>
 
@@ -535,6 +547,15 @@ export default {
       }
     },
 
+    async refresh () {
+      const cache = await caches.open("dougal");
+      for (const key of await cache.keys()) {
+        cache.delete(key);
+      }
+      await this.$root.sleep(300);
+      this.getSequenceData();
+    },
+
     sequencesBBox (margin = 0.1) {
       let [ λ0, φ0, λ1, φ1 ] = [ +Infinity, +Infinity, -Infinity, -Infinity ];