Discard runs that didn't start on the hour

I started a run between hours a few weeks back to let a database
migration finish without interrupting an actual run. This made the graph
illegible by decreasing the smallest duration between two individual
runs, making chartjs unable to automatically determine the best width
for each column (it made them way too thin). Resolved by discarding any
runs that start more than 3 minutes after the start of each hour.

stats-frontend/graphs.html

@@ -65,6 +65,11 @@
           }
         })
 
+        // Discard any activations that didn't start on the hour
+        recentNotifications.activations = recentNotifications.activations.filter(
+          activation => activation["start_timestamp"] % 3600 < 180
+        )
+
         // Bind channels data to activations data
         for (
           let activationIndex = 0;