Several UI improvements and features.

- Added support for filtering location data in a certain area.

- Made date range selection optional.

- A more robust way to detect changes in the location filter.

- Let the timeline graph set the default time ticks.

frontend/src/mixins/LocationQuery.vue

@@ -0,0 +1,32 @@
+<script lang="ts">
+import _ from 'lodash'
+
+import Dates from './Dates.vue'
+import LocationQuery from '../models/LocationQuery'
+
+export default {
+  mixins: [Dates],
+  methods: {
+    isQueryChanged({
+      newValue,
+      oldValue,
+    }: {
+      newValue?: LocationQuery,
+      oldValue?: LocationQuery,
+    }): boolean {
+      return !_.isEqual(
+        {
+          ...(oldValue || {}),
+          startDate: this.normalizeDate(oldValue?.startDate),
+          endDate: this.normalizeDate(oldValue?.endDate),
+        },
+        {
+          ...(newValue || {}),
+          startDate: this.normalizeDate(newValue?.startDate),
+          endDate: this.normalizeDate(newValue?.endDate),
+        }
+      )
+    },
+  }
+}
+</script>